The office of the New York attorney general, Eric Schneiderman, is investigating 13 large retailers over whether increasingly unpredictable and on-call work schedules adopted by some employers in the retail sector violate New York labor laws.

“Our office has received reports that a growing number of employers, particularly in the retail industry, require their hourly workers to work what are sometimes known as “on call shifts” — that is, requiring their employees to call in to work just a few hours in advance, or the night before, to determine whether the worker needs to appear for work that day or the next,” Mr. Schneiderman’s office said in the letters, sent Friday to Gap, Abercrombie & Fitch, Target, J. Crew, Sears, TJX and seven other retailers.

“If the employee is told that his or her services are not needed, the employee will receive no pay for that day,” the letters said. “For many workers, that is too little time to make arrangements for family needs, let alone to find an alternative source of income to compensate for the lost pay.”

The letters give the 13 retailers until May 4 to provide information on how they schedule employee shifts.