The complaint, filed Wednesday in U.S. District Court in Seattle, seeks to overturn a law that voter registrations must match personal information in other government databases.

Plaintiffs in the suit, including a labor union, minority voter groups and anti-poverty activists, also want a judge to bar the state from striking mismatched registrations ahead of the September primary and November general elections.

State elections officials were reviewing the lawsuit and declined immediate comment. But Trova Heffernan, a spokeswoman for Secretary of State Sam Reed, said the matching law was meant to make sure potential voters do not misrepresent their identities.

The law in question directs Reed to compare drivers licenses, state identification cards or Social Security numbers on registration forms with records from state and federal agencies to ensure that a voter's information matches.

Potential voters can't be registered without a proper match. People whose applications are questioned must respond to the state's efforts to verify their identity within 45 days, or they're not included on the rolls.

Washington's law is the strictest among a small number of states with such a requirement, said Justin Levitt, a plaintiffs' attorney from the Brennan Center for Justice at the New York University Law School, which coordinated the lawsuit.

In many other cases, states use matching systems to help administrators clean up the voter rolls, Levitt said. But Washington's approach is uncommon - and, he alleges, unconstitutional - because a person's ability to vote hinges directly on a records match.

That process is fraught with small but serious errors, including improperly filled applications and data-entry mistakes at the bureaucratic level, that could lead to about 20 percent of registrations being unnecessarily spoiled, Levitt said.

The problems could be more pronounced among voters in ethnic minority groups, the lawsuit said, because of confusion on both ends over a person's first and last names.

"Matching is not, in and of itself, a bad thing," he said. "The bad thing is making the match, which is an imperfect process at best, a precondition for voting."

"Given the number of applications we typically see, we're likely to have many thousands of eligible voters wrongly rejected," added Alon Halevy, a University of Washington computer science and engineering professor.

The state law being challenged went into effect Jan. 1, when Reed also launched a new statewide electronic voter database required by federal law to keep track of the state's estimated 3.4 million active voters.

Plaintiffs in the case are the Washington Association of Churches, Washington Association of Community Organizations for Reform Now, Organization of Chinese-Americans of Greater Seattle, Chinese Information and Service Center, Filipino American Political Action Group of Washington, Korean American Voters Alliance, Service Employees International Union Local 775, and Washington Citizen Action.

Levitt said the Brennan Center decided to sue Washington because of its strict law, its relatively large population and the attention garnered by the state's tumultuous 2004 governor's race.

That election put Democrat Chris Gregoire into the governor's mansion by a margin of just 129 votes after a third statewide ballot count. Republicans, believing their candidate Dino Rossi was the rightful victor, challenged the election in court and lost.

Rossi declined to appeal to the state Supreme Court, but bad blood and GOP skepticism of voting systems, notably in Democrat-heavy King County, the state's largest, has not subsided.

Conservative critics have claimed a different problem with the state's voting system: security holes that allow erroneous registrations, improper ballots and double votes.