A proposed class action lawsuit alleges Delta Airlines and AirTran Airways colluded to begin charging customers a $15 fee to check a first bag, according to the Atlanta Journal-Constitution.

The suit filed in U.S. District Court in Atlanta claims AirTran invited Delta to collude on the fee, saying it would begin charging if Delta did so first, which Delta accepted.

In November, Delta said it would begin charging a $15 fee to check a first bag. AirTran said it would introduce a similar fee a week later.

AirTran said it made the decision independently, the Journal-Constitution reported. Delta said it was premature to comment on the suit before it had a chance to review the claim.