WASHINGTON >> When President Donald Trump first floated the idea of “no tax on overtime” at a campaign rally last year, he did not elaborate on how it would work. Could anyone who works more than 40 hours a week claim a tax break? Would overtime pay really be completely tax-free?

The answer to both questions, as it turns out, is no.

Under the sprawling domestic policy bill that Republicans pushed through the House and are preparing to steer through the Senate, the tax break would be limited. It would be available only to Americans who, under federal law, must be paid at a time-and-a-half rate for working any time exceeding 40 hours in a week. That’s a broad group that includes almost all Americans who are paid an hourly wage, but many salaried workers would not be eligible.

And the tax relief would not be total. Americans would still owe payroll taxes, and potentially state income taxes, on their overtime pay. Federal income taxes would be eliminated on those wages, but only on the earnings attributable to the 50% bump in pay — only a third of the money made while working overtime.

Even with those limitations, both critics and supporters of the idea believe the tax break could reshape the American labor market. The White House Council of Economic Advisers expects that the policy will motivate Americans to work more and help strengthen the economy.

Skeptics think the change would primarily drive people to reclassify their earnings or even change jobs in order to file for overtime. They worry that if enough people sought jobs that offer overtime, wages in those positions could eventually fall.

“Ultimately, it’s going to create unintended consequences that incentivize certain behaviors in the labor market and thus create winners and losers from that,” said Emmet Bowling, a labor policy analyst at the American Action Forum, a conservative think tank. “Hourly jobs might become more desirable because of this tax deduction.”

Tax experts give the policy mixed reviews because it treats people in jobs that easily allow overtime differently from those with jobs that do not. Some occupations, like teaching, don’t qualify for overtime pay under federal law, while in other cases, people could work more than 40 hours a week in multiple jobs and not receive the tax break.

Even for occupations in which overtime pay is possible, employees may not be able to control their work schedules and decide for themselves to work overtime. The requirement that overtime hours receive premium pay already discourages companies from asking their employees to work more than 40 hours a week.

Alex Brill, a senior fellow at the conservative American Enterprise Institute, said the tax cut could help lure people to work more hours, and therefore help companies become more productive. But employers would still need to allow it.

“If you’re on a factory floor, not everyone can say, ‘Hey give me overtime,’ and then everyone is fighting over who gets to operate the machinery,” he said. “The schedule needs to be managed.”

Overall, the tax cut would be most valuable for people who could easily set their own schedules, meaning it might ultimately favor white-collar workers. A pair of economists studying a tax exemption for overtime pay in France found that the policy did not affect hours worked overall. Instead, they found that the policy, a version of which was in place from 2007 to 2012, primarily allowed people with flexible schedules to declare more overtime hours.

“These results suggest that the upshot of the de-taxation of overtime hours has essentially been tax optimization, with no real impact on the length of time worked,” wrote the study’s authors, Pierre Cahuc and Stéphane Carcillo. In an interview, Cahuc said it was too easy for some people to manipulate their schedules to save on taxes, and called the policy a “bad idea.”

“Almost no country has this type of policy,” he said, “because it doesn’t make much sense.”

The Republican plan would bar people making more than $160,000 a year from claiming the tax break. That limit, which would increase over time, has allayed fears that rich, sophisticated taxpayers could abuse the policy and blow a giant hole in the budget.

The provision would still be relatively expensive; the nonpartisan Joint Committee on Taxation estimated the cost at $124 billion for just four years of the tax break.