Two class action disputes divided the U.S. Supreme Court yesterday as companies looked to build on the victory they won last year when the justices threw out a nationwide gender-bias suit against Wal-Mart Stores Inc.

Hearing two arguments in Washington, the court's Republican-appointed majority questioned separate efforts to press an antitrust suit against Comcast Corp., the nation's largest cable television company, and a securities fraud case targeting Amgen Inc., the world's largest biotechnology company.

Both cases test the standards for determining whether lawsuits can proceed on a group basis. Of the two, the Amgen case may have the greater impact, potentially erecting a new barrier for shareholders who accuse companies of making misleading statements that affect stock prices.