May 11 (Bloomberg) -- Christine Varney, the top U.S. antitrust official, will call this morning for aggressive prosecution of predatory behavior by companies that dominate some markets, according to people familiar with her plans.

Varney will break with a Justice Department policy adopted under the Bush administration that made it more difficult for government antitrust lawyers to take legal action to block mergers, the people said. She will say that an economic recession isn’t a time to back off on antitrust prosecution, the people said.

Varney is scheduled to lay out her antitrust philosophy in two speeches, one today at the Center for American Progress, a Washington-based policy research group that was founded by former members of the Clinton administration. The group has called for the Justice Department to block the pending merger of Ticketmaster Entertainment Inc. and Live Nation Inc., the two biggest companies in live music.

The second speech will be delivered tomorrow at the U.S. Chamber of Commerce, a lobbying group that represents the interests of businesses.

Varney told the Senate Judiciary Committee in confirmation hearings in March that she intended to be more aggressive than the Justice Department under President George W. Bush in challenging anticompetitive mergers. She said the department should “take a fresh look at what standards we use to measure consolidation” and its effect on competition.

To contact the reporter on this story: Christopher Stern in Washington at cstern3@bloomberg.net.

Last Updated: May 11, 2009 09:21 EDT