A case against Rogers that claims the company's advertising misled consumers about its Chatr discount wireless service resumed in court Tuesday.

The country's Competition Bureau conducted an investigation into claims Rogers made in a Canada-wide advertising campaign in 2010 that Chatr subscribers would have "fewer dropped calls than new wireless carriers" and "no worries about dropped calls."

The bureau said Rogers didn't conduct "adequate and proper tests" to back those claims, and was unfairly discrediting its competitors.

"An extensive review of technical data, obtained from a number of sources, led the bureau to conclude that there is no discernible difference in dropped call rates between Rogers/Chatr and new entrants," the bureau said in a statement.

The bureau filed a lawsuit in November 2010 asking the court to order Rogers to stop the campaign, issue a public apology, pay affected customers compensation and pay a $10-million penalty.

"We take misleading advertising very seriously," competition commissioner Melanie Aitken said. "Consumers deserve accurate information so they can make purchasing decisions with confidence."

Rogers is challenging the hefty fine and the constitutionality of certain provisions in the Competition Act that deal with misleading advertising.

The company says the claim it made in its advertising is based on evidence that demonstrated the superiority of the Chatr service.

"Before launching the campaign, we conducted extensive third-party drive testing of our network that clearly validated our ad claim," spokeswoman Patricia Trott said.

"Drive testing is recognized around the world as the gold standard for comparing the performance of two wireless networks and we have a host of industry experts that substantiate our position."

Last year, Bell Canada agreed to pay the $10-million penalty - the maximum allowed under the Competition Act - after the bureau determined Bell had charged higher prices than advertised for services including home phone, Internet, satellite TV and wireless since December 2007.