(Reuters) — The Republican-led House of Representatives voted on Thursday to ease the Patient Protection and Affordable Care Act's health insurance requirements for employers by approving the first of an expected series of bills aimed at weakening the overall health care reform law.

Only 12 Democrats broke with President Barack Obama to join Republicans in backing a measure that would allow companies to offer health coverage to fewer full-time workers by raising the full-time benchmark to 40 hours of work a week from the 30 hours currently stipulated by the Affordable Care Act.

The 252-172 vote sends the legislation to the new Republican-majority Senate. There was no word on when the Senate might take up the measure, but the bill is unlikely to become law because the White House has threatened to veto it.

Congressional aides and lobbyists said Republican leaders chose the bill as the initial salvo of a new Republican assault on the ACA, believing it would attract enough support from House and Senate Democrats to pressure President Obama into signing it.

Republican leaders hope to unveil a number of bills likely to attract some Democratic support that would repeal the law's taxes on medical devices and health insurers, and drop penalties for individuals who fail to obtain coverage.

But President Obama's veto threat, issued a day ahead of the House vote, appeared to dampen Democratic support for the measure, which was below the 18 lawmakers who crossed the aisle last year when the House voted on an identical bill. Dozens of House Democrats have joined Republicans to pass other anti-ACA legislation in recent years.

The ACA set the benchmark for full-time work at 30 hours a week to ensure that larger numbers of workers would receive coverage under a mandate that requires companies with 50 or more full-time employees to offer health insurance.

Republicans railed against the rule on Thursday, calling it a burden on job creators and warning that it would hurt lower-wage workers by giving employers an incentive to reduce their hours. Supporters of the Republican measure, including retailers and restaurant chains, say most 40-hour workers already have insurance.

Leading Democrats pointed to Congressional Budget Office findings showing that the change, if it became law, would hurt more workers than the 30-hour standard, increase the number of uninsured Americans and expand the federal deficit by $53 billion over 10 years in part by driving more employees to seek government-sponsored health coverage.