Intelligence Committee. Despite being trusted with such high-level secrets, he said, the USDA "can't tell me about an issue that's affecting my constituents. It's troubling."

The U.S. Department of Agriculture has asserted that Rancho "processed diseased animals" without a full inspection. The USDA has not received any reports of illness linked to the meat, the agency said Wednesday.

The USDA probe came to light Jan. 10 when federal agents and Petaluma police converged on the plant on Petaluma Boulevard North.

The first recall, announced Jan. 13, initially covered meat processed on a single day. Rancho expanded the recall Feb. 8 to include all 8.7 million pounds of beef processed at its plant in 2013.

More than 1,600 food distributors in the United States and Canada are now recalling beef and other products made with Rancho meat, including two types of Hot Pockets frozen sandwiches and some frozen hamburger patties sold at Walmart.

On Wednesday, six specific batches of El Monterey's Beef & Cheese Taquitos and Ranchero Steak Tornados, which are distributed in the U.S. and Canada, were added to the recall list. The two products are made by Ruiz Food Products in Dinuba.

Rancho operates the last slaughterhouse for cattle in the North Bay, a small plant that processes both older dairy cows and the niche, pasture-raised beef.

The company announced last week that it has ceased operations at its plant on Petaluma Boulevard North. One of its owners said Rancho undertook the recall "out of an abundance of caution," but declined to answer further questions.

Along with the recall, the USDA has revealed that the department is conducting a two-pronged investigation of the company. Both its Office of Inspector General and its Food Safety and Inspection Service are conducting separate probes of Rancho.

Neither Rancho's owners nor the USDA responded Wednesday to requests for comment on Thompson's concerns.

Following his phone call to the USDA official on Wednesday, Thompson said he has asked to speak directly to Agriculture Secretary Tom Vilsack in order to receive an explanation.

A spokesman for Rep. Jared Huffman, D-San Rafael, said the congressman was traveling and unavailable for comment Wednesday, but he seeks to join in the call with Thompson and Vilsack. The Rancho plant is in Huffman's district.

The USDA's scarcity of public comment on the Rancho recall has surprised those who follow the agency and its oversight of the meat processing industry.

"The lack of information is both unusual and unsettling," said Sarah Klein, a senior attorney on food safety at the Center for Science in the Public Interest in Washington, D.C.

Food safety experts are left to guess at the reasons that would justify a yearlong recall. Was it because the USDA inspection system failed to catch problems for many months, Klein said. Or were the company's records so bad that officials now can't determine which batches of processed beef are safe and which are questionable.

"Either way," she said, "the agency has a lot of questions to answer, as does the company."

Thompson suggested that answers are needed to address any safety concerns and to rebuild public confidence in the meat industry and the government inspection system.

"If there was wrongdoing ... we need to get to the bottom of that," Thompson said.