Lawmakers in the US state of Illinois have written an open letter apologising to advocates of equal marriage in the state because on Friday, the last day in the legislative session, a bill to legalise marriage equality failed to be called for a vote, despite passing in the Senate in February.

The bill’s sponsor Greg Harris wept as he announced that, due to a lack of support, the bill would not be voted on. Mr Harris said he planned to lobby for the bill before the next legislative session in the autumn.

Andy Thayer, equal marriage activist and co-founder of the Gay Liberation Network, said House Speaker Mike Madigan was to blame for the “abject betrayal” of equal marriage supporters.

Saying that Mr Madigan’s sway would have been enough to ensure the safe passage of the bill, he also attacked Mr Harris for not calling the vote on Friday.

It later emerged that Mr Madigan extended the deadline for the bill to August 31.

The letter, sent on Monday, said that the sixteen lawmakers, including Harris, were “extremely disappointed” at Friday’s no vote, but went on to reiterate that “marriage equality is going to happen”.

The letter went on to urge that advocates of equal marriage stay “united”, in order to ensure that “full equality” is achieved, and that “this is not time time for us to splinter”, as the opponents to the measure would want just that.

Concluding, the letter apologised to supporters of the measure to legalise equal marriage who turned out on Friday at the House, to urge lawmakers to vote in favour.

Those signing the bill, all Democrats, represented almost all co-sponsors of the bill: Representative Sam Yingling, Representative Deb Mell, Representative Kelly Cassidy, Representative Ann Williams, Representative Sara Feigneholtz, Representative Maria Antonia Berries, Representative Robert Martwick, Representative Mike Smiddy, Representative Christian Mitchell, Representative Lou Lang, Representative Naomi Jakobsson, Representative Robyn Gabel and Barbara Flynn Currie.

Another Representative, Laura Fine, who is not listed as a co-sponsor, also signed the letter.

It is most likely that the bill will be called in August, when the legislature resumes.

The full letter is available to read below.

Dear Marriage Equality Advocates,

Like you, we are incredibly disappointed about what happened Friday in Springfield. But let’s not forget something very important: Marriage equality is going to happen.

As a community we must come together, assess our strategy, and redouble our efforts in the fight for fundamental fairness. This is not the time for us to splinter – for that is exactly what our opponents want.

The more united we are in the coming days and weeks, the sooner the bill will get passed – and the sooner our dreams of full equality will become a reality.

We want to extend our sincerest apologies to the families who rushed to Springfield in the waning hours of session to support equality in anticipation of this historic vote. You have been and continue to be our inspiration and we pledge to fight together until we achieve full equality for all Illinois families.