The union representing 750 hourly workers locked out of their jobs at a Peterbilt Motor Co. plant in Nashville since September said it plans to file a federal lawsuit against the company today.

Mike Pardue, president of the United Auto Workers (UAW) Local 1832, told The Associated Press that the lawsuit will be announced today outside U.S. District Court.

The 3-1/2-year contract between Peterbilt and the union expired August 30, and the company began the lockout Sept. 3. The two sides have met since then, but mostly to exchange information. Pardue said negotiations are scheduled to resume Friday.

Denton, Texas-based Peterbilt announced in August that it would lay off 500 of the plant's 750 union employees this month, citing a decline in new truck orders. Pardue said the layoff "has something to do" with the lawsuit, but he would not elaborate.

Peterbilt said the layoffs are coming because of a sharp drop in heavy-duty truck orders. Many fleets pre-bought Class 8 trucks before October 1 to avoid trucks equipped with new EPA-compliant engines.

Plant manager Joe Scattergood said he could not comment on the lawsuit until he has more details.