The City of Winnipeg is demanding that an advertisement produced by the Canadian Union of Public Employees be pulled from the airwaves.

The advertisement refers to land transactions and accuses the city of selling off public infrastructure. Part of the ad claims the city sold fire halls "to their friends."

The city has hired a private law firm to send a letter to CUPE Local 500, demanding the union remove the ad immediately.

The city threatens legal action, in the form of a defamation lawsuit, if the ad is not pulled.

But CUPE local president Mike Davidson said the union will not be intimidated.

"We stand by our statement," Davidson said Friday.