ST. PAUL  — For the first time, Minnesota’s Senate plans to vote on a ballot measure aimed at banning gay marriage in the state Constitution.

The vote scheduled for today would put the proposal half way toward the November 2012 ballot, where a majority vote would enact it. The House, which like the Senate is controlled by Republicans, is expected to follow suit.

Proposed constitutional amendments don’t go through the governor, denying Democratic Gov. Mark Dayton a chance to block it.

Groups on both sides of the debate sent out urgent messages to encourage people to contact lawmakers before the vote.

Democrats have long prevented a vote by the full Senate but lost their governing majority in the 2010 election.