The opening salvo in the Obamacare fight in the new Republican-controlled Congress has been fired, with the House easily passing a measure Thursday designed to weaken the healthcare law.

The bill seeks to revoke the Affordable Care Act’s provision that companies offer health coverage to employees who work at least 30 hours a week. Instead, the measure stipulates that employees must work 40 hours to be eligible for healthcare benefits.

The bill passed 252 to 172, with 12 Democrats voting yes. No Republican voted in opposition.

Republicans said the 30-hour threshold has caused many struggling Americans to have their work hours cut by employers that can’t afford to provide insurance.

“Businesses are now reacting to Obamacare’s perverse incentive, and scaling down,” said House Majority Leader Kevin McCarthy, R-Calif. “The employer mandate and Obamacre as a whole are hurting the job market and is hurting America. Only a full repeal of this law will solve the problem, but this bill helps.”

But Democrats say that upping the workweek definition will give businesses a legal excuse to stop covering employees who work more than 30 but fewer than 40 hours.

“This bill is nothing more than a tool for large employers to avoid providing their employees with health insurance, despite the fact they can afford to do so,” said Bill Pascrell, D-N.J. “The bill will reduce the number of people receiving insurance through their employers — simple fact."

Democrats also say Republican claims that the 40-hour mandate is hurting small business are bogus because the provision only applies to companies with 50 or more employees.

The measure now goes to the Senate, where new Majority Leader Mitch McConnell, R-Ky., is expected to take up the measure soon. But with Republicans assuming control of the Senate this week, anti-Obamacare measures like the "Save American Workers Act" now have an easier path at clearing Congress and landing on the president's desk.

It’s uncertain if the measure will get the 60 votes likely needed for it to clear the 100-seat chamber. But at least two Democrats, Sens. Joe Manchin of West Virginia and Joe Donnelly of Indiana, have said they will support it.

President Obama has vowed to veto the bill, saying it would significantly increase the deficit, reduce the number of Americans with employer-based health insurance coverage and create incentives for employers to shift their employees to part-time work.

“Rather than attempting once again to repeal or undermine the Affordable Care Act, which the House has tried to do over 50 times, it is time for the Congress to stop fighting old political battles and join the president in forwarding an agenda focused on providing greater economic opportunity and security for middle class families and all those working to be a part of the middle class,” said a White House statement.

The measure would need a two-thirds majority vote in both houses to overcome a veto, a scenario unlikely in the Senate, where Republicans number 54 in the 100-seat chamber.

Still, with Congress now completely in Republican control, the party is eager to ramp up its fight against Obamacare ahead of the 2016 presidential elections. And while a full repeal of the healthcare law is highly unlikely as long as a Democrat is in the White House, measures aimed at weakening or repealing narrow portions of the law unpopular with Republicans could have success — if enough moderate Democrats can be persuaded to break party rank.

Next up on the GOP's anti-Obamacare agenda could be an attempt to repeal a tax on certain medical devices imposed under the healthcare law, which many Democrats oppose. The tax applies to a broad range of products — from pacemakers and dental instruments to surgical gloves — and is one of several taxes built into Obamacare to help pay for its reforms.

A bill introduced in the House last year to repeal the tax garnered about 275 cosponsors in the 435-member House, including 46 Democrats. It passed in September as part of a large jobs package but died in the Democratic-controlled Senate.