Microsoft-Yahoo Deal Would Face Tough Scrutiny

Microsoft Corp.'s $44.6 billion bid for Yahoo Inc. is expected to get a hard look from European and U.S. antitrust enforcers and lawmakers, possibly delaying a completed deal for six months or more.

But merger-law experts predicted that a buyout ultimately would win approval.

The U.S. Justice Department confirmed that it would undertake an antitrust investigation, and members of Congress also said they would study the matter. In Brussels, a European Commission spokesman declined to comment.

The potential effects on online search and advertising would get the most scrutiny, antitrust lawyers said, because the deal combines the second and third-largest ...