Updated

Some of the nation's largest meatpacking companies plan to shut down plants Monday, anticipating many of their workers will attend immigration rallies that day.

The top three beef-producing companies, Tyson Foods (TSN), Swift & Co. and Cargill Inc., all said they were closing plants.

ConAgra Foods Inc. (CAG) said it would honor requests for time off if possible, but did not plan any changes in production.

"We obviously have some employees that this is an important issue and could affect their families, friends and neighbors," said Chris Kircher, a spokesman for Omaha, Neb.-based ConAgra.

National immigrant organizations have been calling on people to skip work and avoid shopping Monday to demonstrate the economic power of immigrants. Rallies calling for less restrictive immigration laws also are being planned around the country that day.

Over the past two months, immigrant advocates have staged rallies and marches in several cities, some drawing tens of thousands of demonstrators, as Congress considers immigration reforms. Congress has been divided over whether to crack down on illegal immigrants or embrace them as vital contributors to the U.S. economy.

Tyson, headquartered in Springdale, Ark., will close 12 plants nationwide, the company said in a statement. Spokesman Gary Mickelson cited "factors such as market conditions that permit scheduling changes and the potential shortage of workers."

Swift, based in Greeley, Colo., will shut down four of its five beef processing plants and two of its three pork processing plants, spokesman Sean McHugh said in a statement Friday. The decision was based on factors including previously scheduled maintenance, general market conditions and employees' requests for time off.

And Cargill, based in Wichita, Kan., will close plants in Iowa, Kansas, Illinois, Texas, Nebraska and Colorado.

Pittsburgh, Texas-based Pilgrim's Pride, planned to adjust its work schedules at poultry plants in Arkansas, while Delaware-based poultry processor Townsends Inc. planned to close its plant in Batesville, Ark., on Monday.

Kircher, the ConAgra spokesman, said the company favors immigration reforms that support employees' rights and the company's ability to comply with federal laws to ensure a legal work force.

Earlier this week, McHugh said Swift supports immigration reforms that "protect employers that comply in good faith with hiring requirements" and that would include border security and guest-worker measures.