BOSTON -- U.S. Reps. John Tierney and Michael Capuano plan to vote in favor of a sweeping overhaul of the nation's health care system, giving Democrats the support of all but one Massachusetts congressman before Sunday's decisive vote.

Reps. Ed Markey, Barney Frank, Jim McGovern, Richard Neal, John Olver, William Delahunt and Niki Tsongas are all backing the bill.

Rep. Stephen Lynch, a South Boston Democrat, remains opposed to the measure, which would extend coverage to an estimated 32 million uninsured, bar insurers from denying coverage on the basis of existing medical conditions and cut federal deficits by an estimated $138 billion over a decade.

Congressional analysts estimate the cost of the legislation would be $940 billion over a decade. Republicans remain unanimously opposed to the bill, citing its cost and reach.

Lynch was one of the first Democrats who had formerly supported the bill to announce he would oppose it in Sunday's vote. Lynch said he did so despite a telephoned appeal from Vicki Kennedy, whose late husband, Sen. Edward M. Kennedy, championed health care for decades. Massachusetts unions responded with a scathing letter, released Saturday.

"Congressman, we will not be able to explain to the working women and men of our union why you voted against their interests," said the letter, signed by Robert Haynes, president of the Massachusetts AFL-CIO and other labor leaders.