ST. PAUL  — Republicans asked a Minnesota court to block a new online voter registration system Monday, saying it was illegally created by the state’s Democratic elections chief.

Four GOP lawmakers and a pair of conservative groups filed a lawsuit seeking to suspend the Web-based system pending legislative action next year. In announcing the action, the plaintiffs said the system raises doubts about the integrity of today’s municipal elections.

It was implemented by Secretary of State Mark Ritchie this fall and has been used by more than 1,900 people to newly register or modify an existing registration.

The plaintiffs said they aren’t opposed to the concept but contend Ritchie lacked the authority to unilaterally launch the system. They said they are worried about data security and voter verification and argued the plan should have been vetted by the Legislature on the front end.

“Online registration could be the best thing since sliced bread. It could be the worst thing since the plague. We don’t know,” said state Rep. Steve Drazkowski, R-Mazeppa.

Ritchie’s office responded to the lawsuit with a prepared statement expressing confidence that “we are on firm legal ground providing eligible voters with common sense tools based in Minnesota law.”

Minnesota is the 15th state to allow online registration. People using the system must present verifiable identification data; their applications will be checked in similar fashion as before.

Ritchie has argued that previous laws gave his office the go-ahead to accept digital documents in the same way it does standard paper forms.

He has said it should provide extra convenience to voters, reduce errors caused by illegible handwriting and incomplete forms and save governments money by cutting down on postage, printing and manual data entry.

Cities and school districts across the state are holding elections Tuesday, including a wide-open race for Minneapolis mayor involving 35 candidates and a nontraditional vote-ranking process. Erick Kaardal, an attorney hired by plaintiffs in the lawsuit, said the online registrations could be an issue if any close contests provoke recounts or legal challenges with ballots by those who registered that way being called into question.

The case was filed in Ramsey County District Court. It is being paid for by the Minnesota Voters Alliance and Minnesota Majority, two groups that have previously clashed with Ritchie over his execution of elections. They have asked the court to force the state to pay their legal fees if the case succeeds.

No Democrats are among the legislators who are suing but some have joined in calling for legislative scrutiny.

The plaintiff’s attorneys want to fast-track the case and hope to have it heard in court before mid-December.