Gov. Scott Walker's campaign and the head of the Wisconsin Republican Party sued the state elections board on Thursday, saying its process for reviewing signatures on recall petitions is unconstitutional.

The lawsuit asks a judge to order the Government Accountability Board to look for and eliminate duplicative signatures, obviously fake names such as Mickey Mouse, and signatures with clearly illegible signatures. The board argues that state law places the burden of challenging those signatures on the office holder being targeted for recall.

Allowing multiple signatures is a violation of the equal protection clause of the U.S. Constitution because it harms the rights of those not signing, the lawsuit argues.

"The decision of one individual who chooses to sign a recall petition should not carry more weight than the decision of another who chooses not to sign," said Stephan Thompson, executive director of the Republican Party of Wisconsin. "This lawsuit seeks to protect the Wisconsin electors whose voices have been trumped by those purposefully signing multiple petitions."

Board director Kevin Kennedy defended the review process, noting it has been used for two decades.

"The plaintiffs are challenging the rules that have been established by statutes and administrative code, and which have been in place since the late 1980s," he said. "Since then, these rules have been used in every state and local recall petition effort against incumbents of both parties."

Kennedy said in a memo released on Wednesday that doing a more detailed review to toss duplicate and fake signatures would require a change in the law and more resources to the board.

The lawsuit comes on the same day that petition circulators said they had collected 507,000 signatures in one month to force a recall election against Walker. They need 540,208 by Jan. 17.

The GAB has been under fire for saying state law places the burden on challengers to contest multiple or problematic signatures, not the board. Its procedure for reviewing the signatures is to check only for a signature, a Wisconsin address and a proper date that falls within the signature collection period.

Board director Kevin Kennedy released a detailed statement on Wednesday explaining the board's process for reviewing the signatures. It came after a Tuesday board meeting in which staff said signatures of Mickey Mouse or Adolf Hitler would not be automatically struck as long as they are properly dated and have a Wisconsin address.

"Wisconsin law requires the GAB to presume that petition signatures are valid, which means that the staff cannot automatically strike names that might appear to be fake," Kennedy said in that statement. "That level of review would require a change in law as well as much greater resources than are available or practical."

He noted that in the review of about 215,000 signatures on recall petitions this summer targeting nine state senators, only a handful were dismissed because they were made up or belonged to dead people. The dismissals came after the names were challenged by those targeted for recalls.