The 3M Co. has filed a lawsuit against one of its former law firms, claiming its attorneys were motivated by "greed" when they switched sides in an environmental case against the conglomerate.

3M is suing Covington & Burling which is helping the state with a lawsuit against the company for environmental damage, allegedly caused by a chemical made by 3M and found in the Mississippi River and several lakes.

The Minnesota attorney general says the law firm agreed to help the state only after its work with 3M was finished. A statement from Covington says the firm had no "active matters" with 3M when it decided to help the attorney general in its case against the company.