Tyson Foods Inc., the world''s largest meat producer, temporarily shut down nine of its beef and pork plants May 1 because many of its workers planned to attend immigration rallies, the Associated Press reports. National immigrant organizations called on people to skip work and avoid shopping May 1 to demonstrate the economic power of immigrants. Rallies calling for less restrictive immigration laws were also 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.