General Motors Corp. (GM) on Tuesday said it was extending its "Employee Discount for Everyone" consumer incentives program through Aug. 1, a move expected to intensify the auto industry's price war.

Under the program, which was launched last month and due to expire July 5, the world's largest automaker is selling anybody a new car or truck at the same lower price a GM employee would pay.

The marketing campaign, which could put a squeeze on profit margins across the industry, drove GM's U.S. sales up 41 percent in June, making it the company's best sales month in 19 years.

The campaign also boosted GM's market share, offsetting sales declines that contributed to its $1.1 billion loss in the first quarter.

The campaign hurt GM's cross-town Detroit rivals, however, and the Chrysler unit of DaimlerChrysler (DCX) has said it will respond by rolling out its own employee pricing program on Wednesday.

Ford Motor Co. (F) may also match the GM program, although a spokesman said on Tuesday that no final decisions had been made yet.

Paul Ballew, GM's head of global market and industry analysis, told reporters and analysts on a conference call last Friday that GM's cost of incentives were flat or up only slightly in June compared to May.

But Autodata Corp. of Woodcliff Lake, N.J., said GM's June incentives increased about 11 percent over the previous month to an industry-leading average of $4,458 per vehicle.