All of the senators joined thousands of pro-labor demonstrators outside the state capitol Saturday.
Protesters criticized Republican Gov. Scott Walker, who signed a bill removing public workers' rights to bargain for anything except wages on Friday.
Police and firefighters are exempt.
Walker says ending collective bargaining helps the state and local government units cut budget deficits.
Recall drives are underway against some Republican Senators who backed the bill, and some of the Democratic senators who left Wisconsin.