SAN DIEGO - Federal investigators were reported to be looking into whether any child labor laws were violated when groups of San Diego Unified students volunteered at Chargers games in exchange for contribution to student organizations.

On multiple occasions, the students assisted with checking tickets, showing fans to their seats and performed other low-level jobs, according to U-T San Diego. Citing district records now being combed through by the U.S. Department of Labor, the newspaper reported at least one group of students was paid $40 per student shift, lasting up to nine hours at a time, or as little as $4.50 an hour.

Investigators appeared to be zeroing in on a group-labor contract between the San Diego High School Associated Student Body and Elite Show Services, the staffing company that provides security and ushering at home Chargers games, U-T San Diego reported. Similar contracts also apparently being looked at involve Clairemont, Mission Bay, Serra and University City high schools.

"We are fully cooperating and working with the Department of Labor to provide the information they have asked for," Bernie Rhinerson, chief of staff for San Diego schools, told U-T San Diego.

The newspaper reported the investigation period covers a two-year span ending last October.

What triggered the probe wasn't immediately revealed.