July 25 (Reuters) - 3M Company sued Covington & Burling on Tuesday, claiming the firm breached its legal duties by dropping the tech giant as a client and then taking on an environmental lawsuit against it for the Minnesota attorney general.

Filed in U.S. District Court in Minneapolis, the lawsuit comes on the heels of an attempt by 3M to disqualify Covington from representing the Minnesota attorney general in her suit accusing 3M of polluting the state's ground and surface water.

"Covington switched its position from arguing (truthfully) on 3M's behalf that environmental exposure to FCs do not pose a risk to humans, to now arguing on behalf of the State that environmental exposure to those very same FCs are toxic," 3M said in the complaint. FCs refer to fluorochemicals. "The breach of loyalty could not be more sharply drawn."

The lawsuit alleges breach of fiduciary duty and breach of contract. It seeks consequential and compensatory damages and the return of any legal fees it has paid Covington since 1992. It also seeks an injunction preventing the law firm from "further jeopardizing 3M's confidential information."

A spokeswoman for Covington had no immediate comment.

PFC BUSINESS

According to its complaint, the company behind Scotch Tape and Post-it Note Pads has a relationship with Covington that stretches back to the 1980s.

Among other matters, the firm advised 3M in its attempts to convince the Food and Drug Administration that two of its food-packaging products under the Scotchban brand were microwave-safe.

3M said it continued to turn to Covington through the 1990s for work relating to the fluorochemical business that had to go before the FDA and the Environmental Protection Agency.

"On behalf of 3M, Covington forcefully advocated that, as both 3M-funded and independently-conducted science shows, PFCs are not unsafe for humans as a result of environmental exposure," 3M said in the complaint.

From 2000 to 2006, Covington also advised 3M as the company began phasing out the use of perfluorinated chemicals, or PFCs.

In 2010, though, 3M said Covington began talking to the office of Minnesota Attorney General Lori Swanson about representing the state in an environmental lawsuit against 3M claiming the company's fluorochemical waste polluted state waters.

At the time, the only active legal matter the complaint mentioned Covington handling for 3M involved the company's employee benefits program. The contract for that engagement, signed in May 2010, stipulated that the law firm needed to alert 3M immediately if Covington even considered taking on a client adverse to 3M.

Instead, 3M received a letter in December 2010 from Covington partner Seth Safra asking for written confirmation that its engagement on the employment matter was done. The letter did not disclose that Covington had been consulting with Swanson's office, the complaint said.

Eight days later, Swanson's office hired Covington. The state filed the lawsuit later that month.

"As detailed in the complaint, 3M believes that Covington & Burling betrayed the most fundamental principles of the attorney-client relationship -- the duties of loyalty and confidentiality," William Brewer III, a partner at Bickel & Brewer and lead counsel for 3M, said in a statement.

The Minnesota lawsuit, filed in Hennepin County District Court in December 2010, could be lucrative for the firm. A copy of Covington's contract with the state shows it would earn 25 percent of the first $75 million recovered, 20 percent of the next $75 million and 15 percent of anything over $150 million if the case settles before trial.

The case is 3M Company v. Covington & Burling, U.S. District Court for the District of Minnesota, No. 12-cv-01800

For 3M: William Brewer III, Bickel & Brewer.

For Covington: Not immediately known.

(Reporting by Nate Raymond)

Follow us on Twitter @ReutersLegal | Like us on Facebook