The Supreme Court on Monday agreed to hear two major challenges brought by corporate interests, including whether more than 1.5 million female employees of Wal-Mart can go forward with the largest discrimination class-action suit in the country's history.

The court accepted Wal-Mart's petition seeking to stop before trial a suit that alleges women were turned down for promotions and paid less than men. The business community has said whether such a huge and diverse group can pursue a class-action suit is one of the most crucial issues facing the court this term.

In addition, the court said it would review a massive environmental suit by eight states, New York City and others targeting power companies for carbon dioxide emissions the states say contribute to global warming.

In both cases, corporations are challenging decisions by federal appeals courts that the suits can go forward. They come before a court that traditionally has been sympathetic to business interests, but is sensitive about recent criticism from the left that it favors corporations over consumer and environmental groups.

In the Wal-Mart case, the justices will not decide the merits of the claims, but looking at the question of whether a single suit is proper when the charges are spread across thousands of stores across the country and involve women in many different jobs.

But the decision about whether a class action suit is allowed could be as important as the veracity of the discrimination claims, and business groups and civil rights activists are squaring off over the implications of the case.

Business groups say certification of a class action puts enormous pressure on a company to settle, regardless of whether the charges can be proved, because of the cost of the litigation and the potential award. For Wal-Mart, the nation's largest employer, the sum could be billions of dollars.

But civil rights groups say class-action suits are the most effective and cost-efficient way to make sure a business ends discriminatory practices and pays a price for its actions.

Theodore J. Boutrous Jr., lead counsel for Wal-Mart, said Monday in a statement that "the current confusion in class-action law is harmful for everyone - employers, employees, businesses of all types and sizes, and the civil justice system."

Laywers for the women said they were "confident that the court will agree that the women of Wal-Mart are entitled to their day in court."

The plaintiffs' lead co-counsel, Joseph M. Sellers of Washington, said the decisions of a district judge in California and the U.S. Court of Appeals for the 9th Circuit allowing the suit to move forward were "based on a vast body of evidence (and) we are confident that the decision to certify the class was sound."

The case began in California in 2001, when lawyers filed suit on behalf of six current and former female employees led by Betty Dukes, a Wal-Mart greeter in Pittsburg, Calif. They represent women who worked at Wal-Mart and Sam's Club stores since December 1998.