HOUSTON — Shipley Do-Nut Flour and Supply Company Inc. pleaded guilty Friday to conspiring to harbor illegal immigrants and agreed to pay a $1.3 million forfeiture to the government, federal prosecutors said.

Three former and current managers of the Houston company also pleaded guilty Friday to hiring or continuing to hire illegal aliens. The case is part of a government attempt to crackdown on employers who hire illegal immigrants.

The company pleaded guilty through its president, Lawrence Shipley III, to conspiring to harbor illegal immigrants.

Sentencing is scheduled for Dec. 19. Shipley Do-Nut faces a maximum fine of $500,000 and up to five years probation then.

As part of the plea deal, the company also agreed to implement new procedures to prevent future violations of federal immigration laws, the U.S. Attorney’s Office said.

On Friday, Jimmy Rivera, 54, a former warehouse manager; Julian Garcia, 38, the current warehouse manager; and Christopher Halsey, 36, the current warehouse supervisor for Shipley Do-Nut, pleaded guilty to misdemeanor charges of hiring or continuing to hire illegal aliens.

All three men have been convicted and sentenced to six months probation. Halsey, Rivera and Garcia were fined $1,000, $1,500 and $2,000, respectively.

Shipley, 41, pleaded guilty last week to continuing to hire illegal aliens and was sentenced to a similar probationary term and fined $6,000.

The guilty pleas are the result of a criminal investigation conducted by Immigration and Customs Enforcement agents.

ICE began investigating Shipley Do-Nuts in January after an employment discrimination suit against the doughnut-maker ended.  Transcripts and other documents from that case showed the company knew it was hiring undocumented workers, said special agent in charge Robert Rutt of ICE’s Office of Investigations in Houston.

In April, agents raided the company’s Houston headquarters and plant and arrested 27 illegal immigrants, including some who lived in an employee dormitory.

ICE found Shipley Do-Nuts owned properties where many illegal immigrant workers lived. The amount the company forfeited was equal to the properties’ value, Rutt said.

Shipley, the grandson of the company’s founder, has been president of the doughnut maker since 2005, when he inherited it from his father. Investigators contend he allowed a pattern of illegal hiring to continue under his tenure.

A Shipley Do-Nuts spokesperson could not be reached for comment late Friday, but a statement posted on the company’s Web site last week said it is “committed to good citizenship” and “continuing to cooperate with government authorities on matters of immigration compliance.”