The U.S. Supreme Court has given the nation's second largest employer a sweeping victory by ruling that a multi-billion-dollar class action discrimination lawsuit cannot proceed because it lacks "convincing proof of a companywide discrimination pay and promotion policy."

The suit against Wal-Mart was cobbled together to represent 1.5 million female and minority employees, all claiming discrimination in pay and promotion.

Henceforth class action lawsuits will have to be smaller or meet the Supreme Court's new standard to proceed, court observers concluded.

"This significantly changes the balance between employers and employees," said Columbia University law professor John Coffee. "And it largely eliminates the monetary threat facing big employers."

The 5-4 opinion in Wal-Mart Stores, Inc. v. Dukes was written by Justice Antonin Scalia.