A Chicago federal judge on Monday ordered Yahoo Inc to face a class action lawsuit accusing the Internet company of sending unsolicited text messages in breach of the Telephone Consumer Protection Act to Sprint Corp cell phone users.

Shah rejected Yahoo’s arguments a class action could subject it to damages which were disproportionate to the alleged damage, encourage “piecemeal” litigation covering other time periods and mobile carriers, and thwart Congress’ desire that claims be brought separately in little claims court.

More than 500,000 cell phone users could be part of the group, court documents reveal.

They said the welcome messages made up unauthorised advertisements for Yahoo services, breaking the national TCPA and subjecting the Sunnyvale, California-based firm to damages of up to $1,500 (about Rs. 99,000) per message if the infringements were wilful.

The case was brought by Rachel Johnson, an Illinois resident who promised to get a welcome message from Yahoo after being sent a junk text message from a different user marketing a way to reduce high-cost debt.

Shah declined to certify another category of T-Mobile US Inc cell phone users for welcome messages. He said the suggested plaintiff in that portion of the case had accepted to receiving messages that were welcome.

Yahoo didn’t immediately respond to requests for comment.

“We value the court’s extensive investigation.”