The other defendants being sued include two other airlines - United Airlines and Alitalia - and ground-handling companies Swissport and Air Menzies.

Documents filed in the Illinois state court last week name 10 plaintiffs, all temporary workers who handled jobs such as loading cargo and food for flights.

Many of them earned a minimum wage of US$7.50 (S$10.20) per hour and some claimed they had not been paid for several weeks.

Their lawyer, Mr Jed Untereker, said the number of plaintiffs could swell in the coming weeks or months.

'We believe there are hundreds, maybe thousands, of workers in a similar plight,' he said.

The workers had been hired by employment agency Ideal Staffing Solutions.

The company - which is also being sued - supplied the workers to the other companies named in the lawsuit.

SIA's alleged involvement is through its cargo unit, SIA Cargo.

While the Singapore carrier did not hire any of the workers involved, SIA Cargo's planes at the airport are handled by Swissport which used workers supplied by Ideal Staffing Solutions.

That does not absolve carriers from the responsibility of ensuring worker welfare, said Mr Untereker, a lawyer for Chicago's Working Hands Legal Clinic.

He told The Straits Times in a telephone interview yesterday: 'We hope this case sends a message to all employers - particularly those using temporary staffing workers. If they try to shield themselves from their responsibilities, if they try to hide behind temporary staffing companies and their workers...they will be caught.'

At this stage, it is difficult to say how much money is owed, he said. More details will surface as the lawsuit progresses, he added.

The case came to light in November when immigration officials did a massive sweep of O'Hare airport and arrested temporary immigrant workers with fake identification cards.

Investigations revealed that some of them may not have been paid for several weeks.

If found guilty, the defendants will have to pay a penalty on top of the wages owed.

When contacted, an SIA spokesman said the carrier does not comment on matters before the courts.

karam@sph.com.sg