A recent Bloomberg View op-ed and Politico report have raised questions into whether Melania Trump, a Slovenian immigrant, former supermodel, and wife of the current Republican presidential candidate Donald Trump, was employed legally in the United States in the mid-1990s while she was in a temporary visa status. (The Washington Post also has a good Q-and-A-style rundown of the issues involved.) The op-ed and reports analyzed Ms. Trump’s past statements about her immigration status and juxtaposed them with the fact that it appears she was employed as a model during that period. If Ms. Trump was in the United States with a lawful immigration status and that status authorized her to be employed (for example, if she held an H-1B visa), then there’s really no issue here to discuss. But Ms. Trump’s response on Twitter to the Politico report did not answer the main questions that were raised: what was her visa status and did it authorize employment?

Since the reports were published, Ms. Trump’s former modeling agent has told the Associated Press that he sponsored an H-1B visa—a temporary work visa that allows employment in the United States for up to six years—for her in 1996. But photos she modeled for which have recently surfaced appear to have been taken in the United States in 1995. Without knowing more or being able to look at her immigration records on file at the State Department and Department of Homeland Security (which Ms. Trump could ask for and release, if she wanted to), it is reasonable to conclude that if she was in fact employed in 1995 and 1996—before she was issued an H-1B—it’s entirely possible that she was unlawfully employed while in the United States on a B-1 business visitor visa, a B-2 tourist visa, or a combination B-1/B-2 visa. Those visa statuses don’t permit employment, although a B-1 status might permit certain business activities (including a single, unpaid photo shoot) as long there is no payment from a U.S. source. But even in the case of a B-1, working for an extended period in the United States as a model would raise serious questions under U.S. law.

We will probably never get a final answer on this, but the situation raises a more important issue: there is a severe and troubling lack of government regulation, oversight, and enforcement when it comes to U.S. temporary (also known as “nonimmigrant”) visa programs.

This lack of regulation, oversight, and enforcement comes in two forms. One is that in the main American temporary foreign worker programs programs like the H-2A, H-2B, or H-1B, the Department of Labor (DOL)—which is mainly in charge of the programs—has limited resources to ensure that the rights of migrant workers are respected. And as a recent investigative report revealed, even when DOL does act, its enforcement actions and sanctions often leave a lot to be desired. This matters because temporary foreign workers are tied to one employer, and that employer controls the migrant worker’s visa status. The arrangement makes it difficult for workers with temporary visas to complain when things go wrong, because if they get fired they become instantly deportable, and temporary foreign workers usually arrive in the country already in debt to labor recruiters who helped them secure their temporary job. Thus, for a migrant worker with a temporary visa, getting fired before earning what he or she paid to get the job isn’t a feasible option—that’s why they keep quiet and put up with abuses and exploitation.

The other issue is that in the lesser-known temporary work visa programs like the L-1, J-1, TN, and O-1, there are virtually no enforceable rules regulating foreign workers employed in the U.S. while on these visas—or their employers. As a result, employers don’t have to test the labor market to see if there are any available U.S. workers who might want the jobs that are eventually awarded to temporary visa holders. And employers who hire workers through these visa programs don’t have to pay their foreign employees at least the local average wage for the job—what’s known as the “prevailing wage”—as they would in the H visa programs. Therefore, employers can undercut U.S. wage standards as well as undercut employers who hire local workers and pay the going rate for similar jobs.

And when it comes to government oversight, outside of the H-visa programs, no federal agency is charged with policing employers who hire temporary foreign workers in most of these nonimmigrant visa programs. There aren’t even any rules to enforce. The only time a federal agency might get involved is if (1) DHS investigates a case of visa fraud or (2) DOL investigates after it receives information that an employer isn’t paying the required federal or state minimum wage. Take for example, one case DOL did a good job on that occurred in California’s Silicon Valley. Electronics for Imaging—a company with a market capitalization of over $2 billion—paid its Indian L-1 visa employees $1.21 an hour to install computers. The company only got into trouble because it didn’t pay the workers the California minimum wage at the time—$8.00 an hour. Had EFI paid the minimum wage, it would have been compliant with immigration and labor laws, even though the average hourly wage for workers in the area who installed or repaired computers at the time was $19 or $45 (depending on the exact tasks).

That’s the real scandal: that employers can get away with undercutting U.S. wage standards by hiring workers with virtually unregulated temporary work visas. Employers can degrade American labor standards by paying workers (even workers who are educated, skilled, and technically trained) just the federal minimum wage, when the true market rate for their labor is much higher. But the B visa—which might have authorized Melania Trump to enter the United States—is entirely on another level.

The B-1 visa is for “business visitors” who, for example, come to the United States to attend a meeting or conference, negotiate a contract, or to repair machinery made by a foreign manufacturer—and the B-1 holder is not permitted to be paid a salary by a U.S. source. But federal agency guidance on B-1 visas creates a grey area, by permitting certain work activities that would normally require a work visa. For example, someone may work as a domestic servant with a B-1 visa, or work under certain conditions if the State Department issues them a B-1 visa in lieu of an H-1B visa. No one outside of the State Department knows the names of the employers using B-1 visas or of those using the B-1 “in lieu of” visas, and State won’t release any information about how B-1 visas are being used despite numerous strongly worded letters from the chairman of the Senate Judiciary Committee requesting it.

The B-2 visa is for tourists coming to the visit the United States temporarily and does not permit employment under any circumstances. The B-1/B-2 visa permits both B-1 business visitor activities and tourism. B visas can sometimes be valid for up to 10 years, usually allowing the visa holder to visit the United States for up to six months at a time. In 2015, a combined total of 7.3 million B-1, B-2, and B-1/B-2 visas were issued. Because they are valid for multiple years, the number of all currently valid B visas is much higher, in all likelihood in the tens of millions.

Are foreign visitors who hold B visas unlawfully employed in the U.S. labor market? Yes—and we know this is true because of cases that have been reported in the media. Recent cases include car manufacturer Tesla, which was paying construction workers with B-1/B-2 visas $5 an hour, and Bitmicro Networks, which paid Filipino engineers on B-1 visas $1.66 an hour. In 2011, Infosys was hit with the largest immigration fine ever—$35 million—for using B-1 visas when H-1B visas were required. And Russian engineers have worked at Boeing in Washington state with B-1 visas for two to three months at a time.

Unfortunately, it is impossible to know the true scope of the problem. No one can reasonably estimate how many foreign visitors with B visas are employed, and it would be a herculean task for any federal agency to keep tabs on tens of millions of foreign visitors to find out if they’re working and being paid at least the minimum wage. Officials from Immigration and Customs Enforcement (ICE), the DHS sub-agency in charge of investigating fraudulent uses of B visas in the United States, stated that they investigate “usually only after getting tips from co-workers or U.S. companies who suspect a competitor of illicitly using low-paid foreign workers.” In 2012, “ICE received 38,000 such tips.”

But just because it would be such a huge task to regulate the B visa doesn’t mean the government shouldn’t do anything. There are still very few DHS regulations outlining B visa rules; the government should start by updating existing rules and promulgating new ones that clarify which activities are prohibited or permitted. The State Department’s ambiguous guidance in its Foreign Affairs Manual (FAM) has created arguably ultra vires quasi-work categories without explicit authorization from Congress. Much of the language in the FAM should be improved or deleted.

A June 7 letter from Senator Chuck Grassley (R-IA) addressed to to the departments of Justice, State, Labor and Homeland Security summed it up best:

The manner in which the B visa program is being used and the absence of real oversight and enforcement is a shame. Despite a long and undeniable history of abuse of the program to bring foreign workers into the United States under cover as “business visitors,” regulations and field governance governing the program have not been updated in years. It’s also obvious that investigation of B visa abuses and unauthorized employment of B visa holders is a rock-bottom priority for all of your Departments—with the exception of the Department of Labor, which has been doing some good work in uncovering these abuses.

Until now, few in the media or in government have seemed to care about the lack of labor market enforcement in U.S. temporary visa programs. Perhaps the supermodel wife of a presidential candidate—who may or may not have been employed doing a nude photo shoot without proper work authorization—may finally get the wider public to pay attention.