President Obama would veto Republican legislation that would alter the definition of full-time work under ObamaCare from 30 to 40 hours, the White House said Tuesday.

“This proposed change would actually do a lot of harm, not just to the Affordable Care Act but to a substantial number of workers across the country,” White House press secretary Josh Earnest said.

{mosads}The White House spokesman said the proposed change “would be putting even more workers in a situation where we could see some employers cutting back on their hours to try to avoid the requirement of providing them quality health insurance.”

The bill, set for a vote Thursday in the House, drew more than a dozen Democratic votes when offered last year. It is one of a series of measures — including legislation on the Keystone XL pipeline and a bill requiring a cost-benefit analysis of all regulations — that Republican leaders hope to pass in the early weeks of the new Congress.

Proponents say the 30-hour requirement creates an incentive for companies to reduce part-time workers’ hours to under that limit, rather than the 40 hours traditionally considered full time. Companies that employ 50 or more full-time workers are required under the law to offer those employees health insurance.

“It [has] hurt people’s take-home pay,” Sen. John Barrasso (R-Wyo.) said on Fox News earlier this week. “It made people that work part time have their hours cut to less than 30 hours a week.”

The White House has previously said the GOP bill would increase the U.S. deficit by $74 billion over the next decade and lead 1 million people to lose their employer-provided coverage.

Changing the workweek under the employer mandate is a top priority for the new GOP Congress, but Earnest noted not everyone in the party is onboard.

“Ironically, a couple of conservative thinkers happen to think we’re right,” Earnest said.

Earnest referenced pieces from National Review and The Weekly Standard that opposed changing the 40-hour workweek, both of which were highlighted in a New York Times story on Monday.

The spokesman specifically cited National Review columnist Yural Levin, who warned that the effort could be “worse than doing nothing.”

“I assume there’s no worse criticism that could be leveled by one Republican to another, than to say that something is worse than the Affordable Care Act,” Earnest said.

The workweek measure has also been at the center of a heavy lobbying campaign from powerful business groups such as the Chamber of Commerce, the National Retail Federation and the National Restaurant Association.