A potential class action lawsuit has been filed against Chicago-based daily coupon dealer Groupon.

The complaint, filed Tuesday in federal court in Chicago, challenges the legality of putting expiration dates on a Groupon deal. Groupon sends offers for daily deals at local restaurants or stores.

Clayton Halunen is an attorney who filed the lawsuit. He said Groupon portrays itself as a coupon, but, really, Halunen said it’s a gift certificate, since consumers pay for the discount. And there are laws against having expiration dates on gift certificates.

“The company is deliberately misleading consumers to believe that there is, in fact, an expiration date when there is not or cannot be,” Halunen said.

Illinois law states gift cards must keep their value for at least five years.

At the center of the lawsuit is Illinois resident Eli Johnson. According to the complaint, Johnson bought a Groupon deal for $55 to play a game of Whirleyball with his friends. But the deal expired in six months before he used it.

In the written complaint, Johnson’s attorney wrote that Groupon has illegal expiration dates that are “unconscionably short.”

Johnson is seeking unspecified financial damages.

A Groupon spokeswoman says the company does not comment on pending litigation.