A majority of voters in Minnesota oppose amending the state's constitution to ban gay marriage, a new poll found.

According to the Star Tribune, which commissioned the poll, 55 percent of respondents oppose a constitutional amendment banning gay marriage, while 39 percent are in favor.

On Wednesday, Senate Republicans and one Democrat, Senator Leory Stumpf of Plummer, banded together to approve Republican Senator Warren Limmer's bill that aims to constitutionally define marriage as a heterosexual union. After three hours' worth of often-emotional debate senators approved the constitutional plan with a 30 to 27 vote. A companion House measure has already cleared its first legislative hurdle and is also expected to pass.

If approved, voters would be asked in 2012 to decide on the definition of marriage. Minnesota law already bans gay and lesbian couples from marrying, but supporters say the law remains vulnerable to legal challenges without the amendment.

The new poll reveals a dramatic shift in public sentiment on the issue. In 2004, 58 percent of respondents to the same Minnesota Poll supported a constitutional amendment that would limit marriage to one man and one woman.

The issue in Minnesota breaks down political lines.

A large majority (75%) of Democrats and a majority (57%) of independent voters said they opposed the proposed amendment. However, a larger majority (65%) of Republicans support its passage.

The paper contacted 806 Minnesotans for its survey, which has a sampling error of plus or minus 4.7 percentage points.