WASHINGTON — A federal investigation into possible food price-fixing has been expanded to include two major industries, tomato processing and egg products.

The Justice Department confirmed Tuesday that prosecutors are conducting separate inquiries into whether the tomato and egg industries engaged in anticompetitive practices.

Federal prosecutors also have been looking at possible price-fixing in the citrus industry for at least a year.

Justice spokeswoman Gina Talamona confirmed the probes.

Although federal law bars competitors from collaborating when setting their prices, Congress has created antitrust exemptions intended to help small farm groups and cooperatives bargain with large food processors.

Inquiries into whether food producers overstepped those limits are being run by federal prosecutors in Sacramento, Calif., and an antitrust division of the Justice Department based in Philadelphia.

Two egg producers in Minnesota — Golden Oval Eggs and Michael Foods — noted in filings with the SEC this spring that they had been subpoenaed by the U.S. Attorney's Office in the Eastern District of Pennsylvania.

The subpoenas requested documents for the period between Jan. 1, 2002 through March 27, 2008 relating "primarily to the pricing, marketing, and sales of our egg products," both companies wrote in their 10-Q filings.

Both companies said in the SEC filings that they intended to cooperate.

Sandie Wohlman, executive assistant of Golden Oval Eggs of Renville, Minn., referred questions on Tuesday to an attorney, who did not immediately respond to an e-mail seeking an interview.

Mark Witmer, treasurer and secretary of Michael Foods Inc., in Minnetonka, Minn., said: "We have fully responded to the request for information." When asked about Michael Foods' exports and domestic production, Witmer said "that's not something we disclose."

Associated Press reporter Amy Forliti contributed from Minneapolis.