The president of the National Organisation for Marriage has admitted he is “disappointed” that the group’s plans for a rally next week haven’t received much attention.

The group’s ‘March for Marriage’ event, which will take place in DC on June 19, has attracted high-profile guests including failed Republican presidential candidates Rick Santorum and Mike Huckabee.

Last week, NOM president Brian Brown sent an email ‘begging’ the group’s members to show up to the event, worrying about a poor turnout in front of the media.

He has this week admitted it is “disappointing” how few people know about the event, and suggested people donate to the group so they can enact a media campaign

He wrote: “I had a disappointing experience yesterday. In speaking to two of my friends I learned that they did not know about the March for Marriage on June 19th!

“I was shocked and it impressed on me how much more promotion NOM needs to do in the final days before the March on June 19th.

“We need to get the word out far and wide — through email appeals, local print, radio, television and online advertising… all of which require a substantial investment.

“Please, in these closing days, will you make a sacrificial donation to the March for Marriage so that we can let the American people know about this incredible opportunity to make their voices heard in the halls-of-power?”

The rally will be followed by a gala for which tickets cost up to $15,000 (£8960).

Last month, NOM had its bid to intervene in an Oregon court case thrown out, after it admitted in legal filings that it could not find a single person with legal standing in the state to publicly back their involvement.

Also last month the Maine Ethics Commission ordered the group to finally reveal a list of its donors, which it had kept private in violation of political donation laws.

The group is yet to comply fully with the ruling.