“You’ve seen the intent by some to challenge this on legislative grounds. I don’t think it will be successful.” Robert Gibbs, the White House press secretary, told reporters.

The US Senate must still pass a Reconciliation or "fix-it" bill that would detail how to pay for health care reform. Republican politicians are also promising to use a number of parliamentary objections to try and stall its passage in the Senate, and are threatening to undo the measure.

The approval fulfils a goal that had eluded many US presidents for a century - most recently Bill Clinton in 1994.

Republican opposition

Republican critics said the $940 billion legislation was a heavy-handed intrusion in the healthcare sector that will drive up costs, increase the budget deficit and reduce patients' choices.

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They also say they would fight a package of changes designed to improve the bill, which will be taken up in the Senate this week, and lead a charge to repeal the bill after reclaiming Congress from the Democrats in November's elections.

"We will challenge this all over America, and the will of the people will be heard," John McCain, a Republican senator said.

Republicans said they would challenge the changes to the overhaul on parliamentary points of order that, if upheld, could send the revisions back to the House.

At least 11 states, including Florida, Michigan and Alabama, plan to come together in a collective lawsuit claiming the reforms infringe on state powers.

"If the president signs this bill into law, we will file a lawsuit to protect the rights and the interests of American citizens," Florida Attorney General Bill McCollum, a Republican, said.

The US president was at his lowest point in public opinion polls, 15 months into his presidency, and there were questions about whether he would be able to accomplish anything on his domestic agenda if he could not get the healthcare bill passed.

The passage of the bill was also a victory for Democrats, who can now cite it as an accomplishment when they face voters in midterm congressional elections in November.