Democratic U.S. Rep. Tim Walz is leading a new coalition of armed services veterans working to defeat the marriage amendment.

Positioning himself as a leading voice of opposition among the state's Washington delegation, Walz joined Jeff and Lori Wilfahrt to announce the creation of Veterans United. The Wilfahrts' son, Andrew, was an openly gay soldier from Rosemount who was killed in Afghanistan last year.

"To ask a young American to serve this nation, and in the case of Corporal Wilfahrt, to make the ultimate sacrifice, how can we use our sacred constitution to limit the freedom to simply marry the person that they love?" asked Walz, who represents Minnesota's First Congressional District. "Veterans understand selfless service. It's our responsibility to protect them as they have protected us."

Minnesota voters are being asked to decide on a measure that would add language into the state constitution to define marriage as a union between a man and a woman. Minnesota law already forbids same-sex marriage, but supporters argue judges or legislators could change that.

Minnesota for Marriage, the lead group backing the amendment, disagrees with the other side's message to veterans.

"The most important thing to recognize above all is that Corporal Wilfahrt is an American hero," said Autumn Leva, a spokeswoman for Minnesota for Marriage. "However, most Minnesotans disagree with the message that Corporal Wilfahrt's parents and the veterans are promoting because the majority of Minnesotans understand that marriage is the unique union between a man and a woman."

Opponents say the amendment would limit gay and lesbian couples from eventually having the freedom to marry.

"It is not lost on us that Andrew died protecting the freedoms that he himself did not have –- especially the right to marry the person he loved," said Lori Wilfahrt. "We believe that all citizens should have the same freedom to marry. We are voting no to protect freedom for all couples to marry, and we believe it is patriotic to do so."

Veterans United is a partner with Minnesotans United for All Families, the lead group opposing the marriage amendment. The group of 100 veterans will travel the state in the coming weeks urging others to vote no.

Said Jeff Wilfahrt: "Those of you who are veterans: You once took the call, you did your duty, and defended the constitution. Then you did it with arms, this fall you can do it with an ink pen. I urge you to vote no."

With seven weeks before the election, both campaigns are ramping up their efforts.

Minnesota for Marriage is putting up billboards this week and is expected to release its first television advertisment around Oct. 1.

A new Star Tribune Minnesota Poll indicates the race is a dead heat, with 49 percent of respondents supporting the measure and 47 percent opposed.

Constitutional amendments must get more than 50 percent of all ballots cast to be approved.