A public interest law firm is preparing to sue the Canadian owners of a pipeline that ruptured in southern Michigan and dumped hundreds of thousands of gallons of oil into a Kalamazoo River tributary.

The Great Lakes Law Center on Monday sent Enbridge Inc. a notice of intent to file suit if a settlement isn't reached within 60 days. The letter accuses the company of violating the Clean Water Act.

The Detroit-based law center says Enbridge could face more than $26 million in civil penalties based on the Environmental Protection Agency's estimate that the spill exceeds 1 million gallons. The company estimates the total at 820,000 gallons.

A phone message seeking comment was left with Enbridge, which reported the spill a week ago.