It was just this spring that millions of Americans learned they were in for a big raise courtesy of the Obama administration’s long-awaited updating of the federal rules for overtime pay. The threshold for determining whether salaried workers are eligible for automatic time-and-a-half compensation when they work more than 40 hours a week is set to double on Dec. 1 to $47,476, giving a much-needed boost to an estimated 4 million workers.

They can enjoy it while it lasts—if they even receive it at all. It’s looking increasingly likely that a rollback of the overtime rules is squarely in the sights of congressional Republicans and the incoming Trump administration.

This is possible thanks to something called the Congressional Review Act. Among its provisions? Congress can vote to repeal—and a new president can sign off on—legislation rescinding regulations approved by the previous chief executive within 60 legislative days.

I italicized legislative for reason. The same way the phrase “business days” does not account for weekends and legal holidays, legislative days are the days Congress is actually in session. And while your representative is surely hard at work fundraising 365 days a year, actual sessions at the Capitol are something else.

Counting back from the end of the current congressional session, lobbyists and legislative staffers believe the 60-day window will likely stretch all the way to late April or early May of 2016. That’s a problem. The Obama administration released a final version of the overtime rules in mid-May.

Republicans in Congress have made no secret of their disdain for these rules and what they would like to see befall them. They claim that increasing the number of workers eligible for mandatory overtime will cause employers to reduce employee hours, causing income loss. Would that happen? Anything is possible, but it’s worth noting that it’s the same claim conservatives tend to make in the face of almost every minimum wage increase, and the evidence is overwhelming that workers as a whole benefit when their minimum pay is raised. No surprise, a survey released by the National Employment Law Project Action Fund in September found that 76 percent of voters in the seven states they surveyed, which included Arizona, North Carolina, and Pennsylvania, supported the new overtime rules.

That’s not stopping congressional Republicans. Politico reported this past weekend that the congressional Republican leadership is considering ending the current session in early December precisely to ensure it can do away with the overtime regulations under Trump.

Rescinding a pay raise is, of course, political poison. But it’s possible that workers won’t see that boost on Dec. 1, no matter what the law demands. A number of business groups (including the conservative U.S. Chamber of Commerce as well as the National Retail Federation) and 21 states have filed a challenge to the law in federal court, so it’s quite possible the rules will be stayed prior to implementation.

And where is Trump in all of this? He did, after all, campaign as the champion of the working class, the exact sorts of voters likely to benefit from the upgraded overtime regulations. Well, he’s no fan. In an interview this past summer, he claimed he “would love to see a delay or carve-out of sorts for our small business owners.” The Trump transition team did not respond to requests for comment.

Overtime rules, of course, are not the only worthwhile Obama administration effort that could fall victim to these sorts of legislative shenanigans. There are about 100 rules at possible risk, including guidance demanding beefed-up standards governing retirement advice, new nutritional standards for school lunches, and higher protections for consumers purchasing and using prepaid debit cards.

And don’t think the Republicans don’t know it! Under the current rules, Congress needs to vote on each regulation individually. It’s quite likely that will change. Last week, the House passed a bill backed by Republican Rep. Darrell Issa that would allow for multiple rules to be repealed in one single bill. It’s all but certain this bill will be reintroduced early in the next congressional session.

If the overtime regulations are stayed, Walmart managers might be among the few to still benefit from them. The retail giant recently gave store managers earning less than the new threshold a raise totaling several thousand dollars so they could continue to work more than 40 hours a week without receiving overtime pay. This, apparently, is what passes for luck in the United States these days.

Some of the blame, should this come to pass, belongs to the Obama administration itself. In 2001, George W. Bush signed off on a congressional repeal of stringent workplace ergonomic standards issued by Bill Clinton less than a month before the end of his term. It’s an action that’s lived in political infamy ever since—and it’s known that the Obama administration was mindful of the 60-day window. But clearly it wasn’t mindful enough. And now, many of us are now likely to be poorer for it.