SANFORD – Vishay-Sprague Inc., Sanford’s largest employer, will lay off 320 employees in April, the company said.

It was unclear which Vishay workers will be affected. The layoffs will slice the plant’s work force by more than a third. The layoffs will begin April 23 and continue for several weeks, according to a notice Vishay filed with economic development officials.

The layoff notices were prompted by a downturn in the cellular telephone industry, said Richard Grubb, vice president at Vishay Intertechnology in Malverne, Pa., the parent of Vishay-Sprague.

Vishay-Sprague produces capacitors, which are used to store energy and control frequency in electronic equipment, including computers.