A group that opposes marriage rights for gay people has said its intervention in a state election in Iowa is just the start of their campaign.

The National Organisation for Marriage (NOM) came to prominence during the campaign for gay marriage in California, when they pumped millions of dollars into opposing it.

Gay rights advocates have accused the group of accepting large donations from Mormon groups – NOM has refused to release information about its donors.

The group’s executive director, Brian Brown, has announced that after campaigns in Maine and Washington DC, their next target is Iowa.

It legalised marriage for gay couples in April after a unanimous decision by judges at the Iowa Supreme Court that the state’s own Defence of Marriage Act was unconstitutional.

“The Reclaim Iowa Project is a multi-year campaign to pass a state constitutional amendment reversing last spring’s same-sex marriage ruling from the Iowa Supreme Court,” according to a press release from NOM.

“Iowans overwhelmingly oppose same-sex marriage, but a handful of politicians are determined to block any effort to give the people of Iowa a say in the matter.

“According to the latest polling, 67% of Iowans favour putting a marriage amendment on the ballot for a decision by all Iowa voters — not just a handful of judges.

“Over the past several months, with the help of Congressman Steve King, NOM has laid the groundwork for its Reclaim Iowa Project, making over a million automated phone calls to Iowa families, and identifying 100,000 new supporters in Iowa.”

NOM claims its aims are to “protect marriage and the faith communities that sustain it.”

It has launched a 10-day radio and TV ad campaign in support of Republican candidate Stephen Burgmeier, running in Iowa’s special election for state House District 90.

“Over the past several months, we have heard from tens of thousands of Iowans who refuse to stand by and watch marriage be redefined by a handful of judges,” said Mr Brown.

“On September 1st, Iowans from Van Buren, Jefferson, and Wapello counties can send a clear message to Des Moines by electing Stephen Burgmeier, who has made a strong commitment to giving Iowans the chance to vote against same-sex marriage.”

The $100,000 NOM ads will run throughout the district over the remaining 10 days of the campaign. The election is on September 1st.