A prominent traditional marriage group is about half way through its 23-city tour to call on Americans to defend the definition of marriage as between one man and one woman.

The National Organization for Marriage, founded in 2007 amid state battles on the definition of marriage, has so far visited ten cities on its bus tour called the “Summer for Marriage Tour 2010: One Man One Woman.” By the end of this week, NOM will have completed another five cities.

“Marriage is good – don’t mess with marriage,” said Damon Owens, a spokesperson for NOM, at a rally in Indianapolis on Monday. “None of us has the power or the right to define something none of us created.”

NOM’s month-long bus tour across 19 states on the East coast and in the Midwest takes places as a federal judge in California decides whether Proposition 8 – a state amendment defining marriage as between a man and a woman – is constitutional.

During the tour, which began on July 4 in Virginia, advocates are educating and mobilizing Americans to protect the definition of traditional marriage.

Maggie Gallagher, chairman of NOM, told Focus on the Family’s CitizenLink last week that the group – within three years of its founding – has nearly 40,000 donors, 700,000 activists and raises close to $10 million a year.

Gallagher said she hopes to “take back territory” and install new leadership that is friendlier to traditional marriage advocates after the upcoming U.S. election cycle.

“We’re now seeing a colorful movement attempting to ground the law into a lie about human nature,” said Gallagher to CitizenLink. “Two men in a union do not equal a marriage.”

“If the government embraces and uses the power of the law to enforce this lie, the result will not only be the disintegration of our public culture of marriage and the suffering of children, but it will also result in a permanent second-class status for Christians and people of other traditional faiths.”

People of faith and others who oppose same-sex marriage will be seen as “racists or bigots” not only in the public opinion but by the law, she warns.

NOM’s marriage bus tour has met much resistance from same-sex marriage supporters at many of its rallies.

The group Freedom to Marry and its state partners are holding their own events across the country to respond to NOM’s tour. Also called the “Summer for Marriage,” the pro-gay marriage campaign’s motto is “Love + Commitment = Marriage.”

“We launched our Summer for Marriage because we know that we cannot allow the distractions, distortions, and discriminatory agenda of groups like NOM to go unanswered,” wrote Evan Wolfson, executive director of Freedom to marry, in a commentary for The Huffington Post last week.

Wolfson describes NOM’s message as “anti-equality” and its supporters as trying to take away others' rights.

Gallagher, however, argues that same-sex marriage is not a civil right.

“We need to stand up for marriage and communicate that ‘We’re here. We’re not going away. We’re going to stand up for what’s right,” Gallagher said.

NOM’s Summer for Marriage Tour will conclude at the U.S. Capitol in Washington, D.C., on Aug. 15.