In a statement, Republican Party of Wisconsin Executive Director Mark Jefferson called the challenge “an expensive waste of time, couched in hyperbole and hot air.”

“After harassing thousands of Wisconsin citizens in an attempt to intimidate them into removing their signatures, it appears Democrats found only a few hundred signatures to directly challenge, out of 60,000 submitted,” Jefferson said. “Even in the unlikely event their challenges of individuals’ signatures will be upheld, they fall far short of what is needed to prevent recall elections. The three Democrats will stand for election this summer.”

In all, 16 recall efforts were sparked by Walker’s controversial anti-collective bargaining bill, currently tied up in a court battle. Eight Republicans were targeted for voting for the bill, while eight Democrats were targeted for leaving Wisconsin in February to avoid voting on the measure. Only senators who have served at least one year in office are subject to recall.

The bill, which strips most collective bargaining rights from most public employees in Wisconsin, prompted weeks of demonstrations drawing tens of thousands of protesters to the Capitol.