Rep. Jim Oberstar said Thursday he opposes the proposed merger of United and Continental airlines.
Oberstar, a Minnesota Democrat who is chairman of the House Transportation Committee, has sent a letter to the U.S. Justice Department, arguing the agency should block the deal.
Oberstar said the merger would stifle competition and accelerate movement toward the creation of three mega-carriers that dominate air travel worldwide.
"This transaction fundamentally alters the nature of competition in the domestic and international marketplace and should be stopped," Oberstar said. "This is wrong. This is bad for competition. And it will be a disservice to all of aviation domestically and internationally."
Oberstar also opposed the merger of Northwest Airlines and Delta Air Lines, arguing it would reduce competition and spur more airlines to try to combine. That merger won regulatory approval while the Bush administration was still in office.
The deal between Continental and United needs approval from antitrust regulators and shareholders. The companies are hoping to close it by the end of the year.
(The Associated Press contributed to this report.)