MADISON, Wisconsin (Reuters) - Organizers of the petition drive to recall Wisconsin Governor Scott Walker submitted what appeared to be more than enough signatures on Tuesday to force the first-term Republican to defend his seat in a special election.

The group United Wisconsin, which opposes the collective bargaining changes and other measures Walker pushed into law last year, said it gathered more than 1 million signatures to recall the governor by the January 17 deadline -- roughly double the 540,208 signatures required.

In a statement, Brad Courtney, the chairman of the Republican Party of Wisconsin, called the recall effort "shameful" and predicted it would "accomplish nothing but saddle Wisconsin taxpayers with over $9 million in unbudgeted costs" related to the special election.

The filing of the petitions will not automatically result in Walker's removal from office. But if the petitions are certified, Walker will be forced to defend his seat in a special election later this year.

"We very clearly believe there is no challenge -- legal or otherwise -- that would prevent these elections from going forward," said Mike Tate, the head of the Democratic Party of Wisconsin.

So far, a Democrat has not yet emerged to run against Walker, though Milwaukee Mayor Tom Barrett, who ran for governor against Walker in 2010 and Secretary of State Doug La Follette have been mentioned as possible candidates.

As many as 17 Wisconsin state senators -- 11 Republicans and six Democrats -- could face special recall elections this year in contests triggered by last year's fight over union rights and other Republican-backed measures.

Indeed recall organizers on Tuesday also submitted what they said were enough recall petitions on Tuesday to force four Republican state senators, including Senate majority leader Scott Fitzgerald, as well as Lieutenant Governor Rebecca Kleefisch, into special elections defending their seats later this year.

Ryan Lawler, a board member of the United Wisconsin, said the success of the signature gathering effort "represents a crystal clear indication of how strong the appetite is to stop the damage and turmoil that Scott Walker has brought to Wisconsin."

The elections could tip the balance of power in the state Senate, where Republicans currently hold a 17-16 majority.

But they may also provide an early glimpse of how closely fought this November's presidential race will be in key Midwestern states like Wisconsin, where voters backed Barack Obama in 2008 but then handed big victories to Republicans, including Walker, in the 2010 midterms.

(Reporting by Brendan O'Brien; Writing by James B. Kelleher; editing by Paul Thomasch)

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