One of the most prominent cases in Australia involves the sports broadcaster Crocmedia, which is in Federal Circuit Court over the issue. Gemma Smith, at age 20, produced radio programs there, starting her shifts at midnight or later and finishing just before dawn. In the six months she worked there, starting in August 2012, she worked as many as seven days out of 10. She was paid nothing.

Jonathan Wilkinson, starting at age 23, worked about the same hours in his 15 months with Crocmedia. He was paid 2,940 Australian dollars, or about $2,500 at current exchange rates, but should have made almost seven times that amount, the lawsuit says.

Court documents show both should have been paid about 18 Australian dollars an hour under minimum wage laws as casual workers. Crocmedia, which is based in Melbourne, has since paid them but may face fines for breaches of workplace laws when Judge Grant Riethmuller hands down his decision on the lawsuit, filed in June 2013. Mr. Wilkinson was not immediately available for comment; Ms. Smith declined to comment.

“The significant alleged underpayment of vulnerable, young workers and the need to deter employers from such behavior were key factors in the decision to commence legal action,” said Steve Ronson, executive director of the Fair Work Ombudsman, an Australian agency that oversees workplace issues.

Crocmedia’s marketing and communications manager, Leah Grant, said the company could not discuss the case until the judge handed down his decision.