Assistant Attorney General Christine Varney said the department is abandoning legal guidelines put in place by the Bush administration in September 2008. Critics complained the earlier set of instructions made it difficult to pursue antitrust cases against big firms.
Varney laid out the new policy in a speech to the Center for American Progress, a left-leaning think tank.
She said some of the problems in the current economy were due to the lack of enforcement in the previous 10 years--a clear jab at the Bush administration, which, she said, raised too many hurdles to antitrust investigations.
"There was a high cost to standing aside. We must change course and take a new tack," said Varney.
She said her remarks weren't aimed at any particular company, but wanted all big companies to get the message.
"Look, when you become successful and you have market power, however you define it, you need to pay attention to the rules," said Varney.
The new rules are "the clearest way to let everyone know that the Antitrust Division will be aggressively pursuing cases where monopolists try to use their dominance in the marketplace to stifle competition and harm consumers," she said.
The decision would reset the government's antitrust policies to be more in line with those of the Clinton administration, which brought a major action against Microsoft.
Varney said the Obama administration would try to follow the historic lessons of The Great Depression, in pursuing antitrust cases even in a troubled economy.