The White House on Wednesday warned of a presidential veto of a $142.5 billion spending bill if Democrats pushed through an amendment that would block new Labor Department (search) rules about overtime pay.

House Democrats contend that millions of workers could lose their overtime pay (search) under the rules. Lawmakers said they had enough Republican support to approve the amendment, leading the GOP leadership to put off a vote Wednesday.

"They want to pull the bill so they have another chance to twist arms overnight," said Rep. David Obey (search) of Wisconsin. He is the top Democrat on the Appropriations Committee and sponsor of the amendment with Rep. George Miller (search), D-Calif.

The first major overhaul of overtime rules in more than 50 years went into effect Aug. 23. The department said the changes would help lower-paid workers and clarify which white-collar workers are entitled to overtime pay.

The department estimated that 1.3 million workers who earn less than $23,660 a year would become eligible, while about 107,000 white collar workers who earn $100,000 or more could lose eligibility.

But Democrats and labor unions warn that slight changes in the rules' wording could exempt up to 6 million from overtime pay.

The amendment would block all aspects of the rules except those that extend overtime to lower-paid workers.

A White House statement said President Bush's senior advisers would recommend that he veto the spending bill "if it contained any provision prohibiting or altering the Labor Department's enforcement of the final overtime security rule."

The bill being considered is one of the biggest and most important Congress considers every year. It provides money for education, health care, medical research and job training programs.

The chairman of the House Education and the Workforce Committee, Rep. John Boehner, R-Ohio, urged colleagues to reject efforts to undermine the rules. Boehner and Rep. Charlie Norwood, R-Ga., said the rules would strengthen protections for police, firefighters, paramedics, nurses and others.

The issue has come up several times in Congress over the past year. Last May, the Senate, by a 52-47 vote, approved language stating that no worker who currently qualified for overtime should lose that eligibility. A week later House Republicans narrowly blocked a vote on a similar measure.

Obey acknowledged that Republicans, who control both the House and the Senate, could take out any provisions referring to the overtime rules in the final version of the bill. But with worker security an issue as the election nears, "it's a hell of a lot harder for them to strip it out this time."