Six more former workers arrested during a raid of the Swift & Co. meatpacking plant in Cactus pleaded guilty to federal charges this week and could go to prison.

The six entered pleas in federal court in Amarillo on Tuesday, the U.S. Attorney's Office said in a news release issued Wednesday.

Charges against them stem from a December immigration raid at the Swift plant in the Panhandle conducted as part of an investigation into the use of Social Security numbers by illegal immigrants to gain employment.

Four of the defendants -- Jesus Gutierrez-Ramos, Domingo Velasquez-Gutierrez, Manuel Castro-Pablo and Cristino Pablo-Alonzo -- each pleaded guilty to one count of fraud in connection with an immigration document. They face a possible maximum sentence of 10 years in prison and a $250,000 fine.

Two others pleaded guilty to misdemeanor charges of unlawful entry by an illegal immigrant. They face a maximum penalty of six months in prison and a $5,000 fine.

Raids at Swift & Co. plants in six states led to the arrests of more than 1,200 immigrant workers. All 53 people charged in the Northern District of Texas have pleaded guilty. Sentencing has not yet been set.

No charges were filed against Swift, which bills itself as the world's second-largest beef and pork processor.