New York's attorney general has questioned 13 national retailers, including Gap, Target and JC Penney, about "on-call shifts", a staffing practice that requires workers to find out just hours before their shift whether or not they need to report to work.

Attorney general Eric Schneiderman’s letter, sent on Friday, alleges that on-call systems leave “too little time to make arrangements for family needs, let alone to find an alternative source of income to compensate for the lost pay” on days the employees are not called in to work.

Some employers require on-call workers to check by phone, email or text message shortly before their designated shift whether their services are needed that day, according to the letter seen by Reuters.

Practices such as on-call scheduling may violate a New York law, according to the letter. Employers in New York are subject to a rule that says employees who report for a scheduled shift on any day have to be paid for at least four hours at the basic minimum hourly wage.

Letters were also sent to Abercrombie & Fitch, J. Crew, L Brands Inc, Burlington Coat Factory, TJX Cos, Urban Outfitters, Crocs, Ann Inc, Sears Holdings and Williams-Sonoma.

Mr Schneiderman asked the retailers to provide details on the processes they follow to schedule on-call shifts, such as whether they use computerised systems and penalise employees who do not follow on-call procedures.

He also asked the companies for any analysis they may have conducted on cost savings associated with on-call shifts and the impact on workers’ well-being.

“Gap Inc is committed to establishing sustainable scheduling practices,” a spokeswoman said.

The retailer said it was engaged in a research project with the UC Hastings College of Worklife Law to examine workplace scheduling and productivity, and expects to receive some data in the fall of 2015.

“In the meantime, each of our brands also has been working to evaluate and refine their practices to make improvements,” the spokeswoman said.

Target said workers are informed of their schedules 10 days before the start of a work week.

"Target's scheduling practices do not include 'on-call' shifts where team members would be required to call in to see if they are working a given day," spokesman Evan Lapiska said.

The companies have until May 4th to send in their responses.

Representatives of the other 11 retailers did not immediately respond to requests for comment.