A Democratic state senator from New York is to speak at a rally opposing same-sex marriage held by a listed hate group.

Senator Ruben Diaz, who represents the 32nd District in the New York State Senate, has been confirmed as a speaker at the National Organisation for Marriage’s 2015 ‘March for Marriage’ event in Washington DC.

The event – which in 2014 featured a line-up of prominent Republican politicians – has notably downscaled this year, with Senator Diaz the only elected politician set to attend.

Despite the event billing itself as opposing only same-sex marriage, a number of speakers are extremist anti-gay activists, including Mat Staver of the Liberty Council and Josh Duggar of the Family Research Council – both also listed hate groups.

Senator Diaz has previously spoken at a number of anti-gay events – despite being a Democratic state congressman.

He won re-election in 2014 – facing no opponent in the Democratic primary.

Senior Republicans including Rick Santorum, Mike Huckabee and Tim Huelskamp spoke at the event last year – but are all absent from this year’s billing.

It claimed 10,000 people attended the rally last year – despite independent estimates finding that at most 2000 people were there.

Before the event, Brian Brown had sent an email “begging” members to show up to the rally on the day, to avoid embarrassing him in front of the media.

This year’s march will take place on April 25 – the same week that the US Supreme Court begins hearing a case that could decisively bring same-sex marriage to all 50 states.