In filing its challenge to Wisconsin's domestic partnership law, a group opposed to gay rights claims it's too similar to marriage.

“The same-sex only, statewide domestic partnership registry mimics marriage,” Julaine Appling, executive director of Wisconsin Family Action (WFA), told Wisconsin Radio Network.

The case lists four WFA board members as plaintiffs and claims they have been harmed because their tax revenues are being used to fund the registry.

“Plaintiffs and other Wisconsin taxpayers are damaged and injured by Defendants' [the state] expenditure of tax revenues for the implementation and administration of the unconstitutional and illegal domestic-partnership registry, registration system, and Plaintiffs have standing to assert this challenge.”

The group is making good on a promise it made last year to refile its case in a lower court after the Wisconsin Supreme Court refused to block the law's start.

Wisconsin became the first state with a constitutional amendment banning gay marriage to recognize the unions of gay and lesbian couples with domestic partnerships when it approved the law. Registering with the state grants gay and lesbian couples access to 43 rights, most of which center around estate planning and hospital visitation issues.

Governor Jim Doyle, a Democrat, strongly backed passage of the registry.

“The governor and his liberal cohorts created a legal status that is substantially similar to that of marriage,” Appling added.

Wisconsin's gay marriage ban “clearly says that a relationship or a legal status … substantially similar to marriage is not legal in this state,” she claimed.

WFA had also supported passage of the anti-gay marriage amendment as the Family Research Institute. It is being represented by the Christian-based Alliance Defense Fund (ADF). ADF lawyers are also defending California's gay marriage ban, Proposition 8, in federal court.