The Obama administration estimates that 4.2 million workers will either receive raises or protections against being forced to work more than 40 hours a week.  The new law takes effect Dec. 1.

The updating of the overtime rule — the first change since 2004 and the biggest since 1975 — was opposed by Republicans in Congress and many business groups. Lawsuits to delay or kill the new rules are likely, experts say.

The Heating, Air-Conditioning and Refrigeration Distributors International are among the organizations criticizing the new requirements.

“We believe this rule will have a negative impact upon many of our members,” said association CEO Talbot Gee. “At a time when companies are faced with ever-increasing health care and compliance costs, this misguided rule will add another expense to distributors and restrict their ability to offer employees flexibility and opportunity to attend continuing education and professional development events. We strongly urge Congress to exercise its oversight responsibilities and make the Department of Labor take another look at this rule."

Also opposed is the National Association of Home Builders, which urged the GOP-controlled Congress to rescind the regulation.

"Congress can play a constructive role by moving quickly to pass the Protecting Workplace Advancement and Opportunity Act, legislation that would force the agency to withdraw this rule until it has considered the effects it would have on small businesses, consumers, workers and the economy,” said NAHB Chairman Ed Brady.