Mack Trucks plans to add 125 workers at its assembly plant in Macungie, Pa., starting the first week in October.

The move will support a ramp-up in production following a boost in the company's order activity in the highway and refuse sectors, said spokesman John Walsh.

Walsh said the company will recall people that were previously laid off, but it will also need to bring on new employees. Mack would not say how many.

"Beyond the economic and market forces at work, we're also getting a very positive reaction to our new EPA 2010-compliant trucks," Walsh said. "These trucks meet the most stringent environmental regulations in the world -- and in addition to this, they are also offering our customers better fuel economy than pre-2010 models."

Through July, Mack's retail sales were up about 17 percent. Also in July, Mack announced it would supply 325 Mack Pinnacle Model DayCab tractors to Chrysler Group Transport, effectively replacing Chrysler's previous fleet in the U.S. and Canada.

The Macungie plant currently employs about 750, while the Lehigh Valley plant employs 1,000 people.