ST. PAUL, (AP) - A group of Republican lawmakers and conservative activists are suing to stop Minnesota Secretary of State Mark Ritchie from implementing an online voter registration system.

The plaintiffs are planning to hold a press conference Monday at the Capitol. The group includes Sen. Warren Limmer and Rep. Steve Drazkowski as well as representatives of Minnesota Voters Alliance and Minnesota Majority.

Ritchie, a Democrat, launched the Web-based voter registration system this fall. He says current state law gave him the clearance he needed, but some Republican lawmakers say he lacked legislative authority. Gov. Mark Dayton and other fellow Democrats support online voter registration but say Ritchie should have had explicit approval from lawmakers first.

More than 1,500 people have used the system to register or update an existing registration.