A petition against Wisconsin Democratic state senator is on the verge of triggering a recall against him amid fallout of the passage of the state's controversial union law.

The petition against state Sen. Robert Wirch has gathered more than the 13,537 signatures needed to force a recall election, its organizer told The Milwaukee Journal Sentinel

The news came after a recall petition against GOP state Sen. Dan Kapanke was filed on Friday, the first one to be submitted, and it signals that Wisconsin Republicans are pushing back against Democratic efforts to force recalls of several GOP senators with their own campaigns.

Democrats are seeking to flip the state's upper chamber in response to GOP Gov. Scott Walker's union law, which curb collective bargaining rights for unionized state employees and force them to pay part of their health and pension benefits.

The law gained national attention and became the topic of a proxy battle between Republicans and Democrats over fiscal issues.

In order to flip the upper chamber from red to blue, Democrats would need to force recall elections, and then defeat, three GOP senators. But that could be harder if Republicans succeed in recalling any of the eight Democrats eligible this year.

After a recall petition is submitted, a state board as 31 days to review the signatures. It if passes the review, an election can be held as early as six weeks later, but that could be slowed by legal challenges, according to the Journal Sentinel.