Top Senate Democrats have vowed to block a wholesale repeal of the health care reform law passed earlier this year, saying millions of U.S. senior citizens would face the prospect of paying more for prescription drugs if the repeal took place.

The senators said 3.4 million U.S. seniors would be affected by a repeal of the 'donut-hole' fix.

While the election saw Republicans take control of the House of Representatives, Democrats still control the Senate with 51 members and two Independents who caucus with the Democrats. There are 47 Republican senators.

If House Republicans move forward with a repeal of the health care law that threatens consumer benefits like the donut hole fix, we will block it in the Senate, Democrats in leadership positions said in a letter to House Speaker-elect John Boehner, R-OH on Monday.

We urge you to consider the unintended consequences that the law's repeal would have on a number of popular consumer protections that help Middle Class Americans, they wrote.

The senators who signed the letter are Sen. Harry Reid of Nevada, Sen. Dick Durbin of Illinois, Sen. Charles Schumer of New York, Sen. Patty Murray of Washington and Sen. Debbie Stabenow of Michigan.

The federal health care law signed last year - known as the Patient Protection and Affordable Care Act - will close the so-called donut-hole by 2020. It called for seniors to receive a 50-percent discount on name-brand drugs purchases -- when in the coverage gap known as the donut hole -- starting in 2011.

The gap in coverage arises when a Medicare user goes beyond the $3,610 limit for prescription medications. A covered individual then has to spend the next $4,000 out of pocket before they qualifiy for further assistance.