Freightliner plans to cut about 1,500 jobs at its truck-manufacturing plant in Cleveland, N.C., a rural town 45 minutes north of Charlotte.

The Portland-based company says a drop in demand for its heavy trucks has prompted the cuts, which are slated to take effect June 6.

The plant has about 2,900 workers and will go to a single shift from two as a result.

The company says the plant has been operating on a periodic shutdown basis since April 2007 because of higher production costs associated with implementing new federal standards for diesel-engine emissions. A weakening economy has also contributed.

Although Freightliner expects the slowdown in truck orders to continue through the first half of this year, the layoff notice “will be rescinded if market recovery sufficient to support two shifts occurs prior to June 6.”

The company, meanwhile, plans to move its sales and marketing office 19 miles south of Charlotte this year to Fort Mill, S.C. The truckmaker, which recently changed its name to Daimler Trucks North America, has said 118 of the 340 employees of the Portland-based unit have agreed to transfer to the local site.

Freightliner has an 11-year agreement to occupy a 150,000-square-foot building under construction in the area.

Freightliner said in October it would relocate the Portland jobs to South Carolina to be closer to customers and its three production facilities in the Charlotte region. Besides the plant in Cleveland, N.C., Freightliner operates a truck plant in Mount Holly, N.C., and a parts plant in Gastonia, N.C.

The company also is considering a larger shift of corporate employees to South Carolina. It has an option on about 400 acres in Fort Mill.

Freightliner is one of Portland’s largest employers, with roughly 3,170 workers at its Swan Island headquarters.