MADISON, Wis. -- The state Senate passed on Wednesday a bill to amend the Wisconsin Constitution to ban gay marriage and Vermont-style civil unions.

The Senate voted 19-14 to approve the amendment, which now goes to the Assembly.

State lawmakers had expected it to pass there easily, and be on the statewide ballot in November.

The Republican-controlled Senate rejected a series of attempts by Democrats to alter the amendment, including a push to strip the portion pertaining to civil unions. The bill would prohibit legal recognition of any relationship between unmarried people that is identical or substantially similar to marriage.

"We have a responsibility to set the course," said Sen. Scott Fitzgerald, R-Beaver Dam, who is one of the bill's sponsors.

"There has not been, as I said before, one single marriage certification issued to a same-sex (couple) in the state of Wisconsin because we can't because it's illegal already," said Sen. Jon Erpenbach, D-Middleton, who opposed the amendment.

Wisconsin law already defines marriage as a union between a man and a wife, but the amendment's supporters said that they fear a judge could invalidate the statute and order the state to recognize gay marriage, as took place in Massachusetts.

Opponents said that the amendment would write discrimination into the state constitution and could strip gay couples of any legal recognition, such as health care benefits.