ST. CLOUD (AP) - The City of St. Cloud is joining an antitrust lawsuit that accuses companies of fixing the price of a chemical that's used to purify drinking water.

St. Cloud public services director Pat Shea says if the price fixing did occur, it likely cost city taxpayers more than $850,000.

St. Cloud joins Minneapolis, St. Paul, Duluth and Rochester in the class-action lawsuit against the manufacturers and distributors of liquid aluminum sulfate. St. Cloud city attorney Matt Staehling says the community buys between 350 and 585 tons of aluminum sulfate each year. Staehling says the cost per ton nearly doubled over a six-year period.

General Chemical Corp. is one of the defendants. Last fall, a former General Chemical executive pleaded guilty in a case brought by the U.S. Department of Justice to price fixing.