The National Organization For Marriage (NOM) has launched a campaign opposing gay marriage in Minnesota.

The nation's most vocal opponent of giving gay and lesbian couples the right to marry began Tuesday airing a statewide television ad urging voters to call on lawmakers to take up the issue of defining marriage as a heterosexual union in the Minnesota Constitution.

Calling Minnesota “the next key battleground state,” the group said it would spend $200,000 in the state.

“Many Minnesotans are unaware that special interest groups are working to convince activist judges and DFL [Democratic-Farmer-Labor] lawmakers to redefine marriage in the state,” Brian Brown, president of NOM, said in a statement.

The first ad takes aim at four prominent candidates running for governor who support gay marriage: former state Rep. Matt Entenza, independent candidate Tom Horner, former state Senator Mark Dayton and state Rep. Margaret Anderson-Kelliher.

“Leading DFL and independent candidates for governor support homosexual marriage,” a male announcer says in the ad. “And most DFL lawmakers don't want you to have a say. When they ask for your support, ask them if they'll guarantee your right to vote on marriage.”

The campaign arrives just days after three gay couples announced they were suing the state for the right to marry. The couples are challenging the state's 1997 Defense of Marriage Act,which defines marriage as a heterosexual union.

State lawmakers have also introduced gay marriage bills.

The campaign was praised by Tom Prichard, president of the Minnesota Family Council, a group that opposes gay marriage.

“We welcome NOM to Minnesota and appreciate their efforts to inform Minnesotans on the serious threat to marriage in our state,” he said. “Marriage bonds mothers and fathers to one another and children to their parents. The well-being of society is at stake when the institution of marriage is attacked.”

NOM is also spending heavily in California, where the group first made its mark leading the effort to pass the state's gay marriage ban, Proposition 8, in 2008. In a $300,000 media buy, the group attacks former Congressman Tom Campbell who is running for the GOP nomination for the US Senate, calling him and his Democratic rival Senator Barbara Boxer “two peas, same liberal pod” because they both support gay marriage.

Over the past year, the group has also influenced races in New York, Massachusetts and Iowa, where it supported candidates based on the single issue of gay marriage, at times over the objection of the Republican Party.

“Our goal is not to necessarily elect Republicans,” Brown told The Associated Press. “Our goal is to elect candidates who will stand up and protect marriage.”