Top Democrats in the U.S. Senate are warning House Speaker-elect John Boehner they'll block any Republican effort to repeal President Barack Obama's health-care overhaul.

Senate Majority Leader Harry Reid, shown in a December photo, said Monday that Democrats will block Republican efforts to repeal U.S. President Barack Obama's health-care legislation. (Associated Press) Republican leaders in the new House announced Monday that they'll hold a vote on Jan. 12 to repeal the measure, setting the stage for a showdown with the Democratic-controlled Senate.

Senate Majority Leader Harry Reid of Nevada said earlier Monday that Democrats in the Senate would thwart any attempt to repeal the landmark legislation, which extends coverage to more than 30 million uninsured people.

Citing better Medicare prescription coverage and other changes in the new law, Reid and his top lieutenants say in a letter the overhaul "is too important to be treated as collateral damage in a partisan mission to repeal health care."

The letter says repeal would have "unintended consequences" for the part of the law that gradually closes the Medicare prescription drug coverage gap, as well as for other popular consumer benefits.

Also signing the letter are senators Dick Durbin of Illinois, Charles Schumer of New York and Patty Murray of Washington.

A spokesman for the No. 2 House Republican, Representative Eric Cantor, said the health-care law is a "job killer for businesses small and large," but Reid said Republicans are on a "partisan mission."