The UK's decision to split from the EU is a "dangerous moment for progressive values", Frances O'Grady will warn. The Trades Union Congress (TUC) general secretary, who campaigned for a Remain vote at the EU referendum, is expected to address the Brexit result at London's annual LGBT festival, Pride, on 25 June.
"There's never been more need for solidarity than now," O'Grady will say. "Two days ago the people of this country made the momentous decision to leave the EU. And the implications will be felt for a generation to come.
"Make no mistake, this is a dangerous moment for all of us who believe in progressive values. So many of the rights we fought so hard to win from Europe are now at risk.
"Not just rights at work, but equality rights which make a difference to women, black people, disabled people and LGBT people.
"And we must be resolute in defending them from a government that is about to take a sharp turn to the right. And that means working together – the trade union movement, the LGBT community, each and every one of us here today.
She will add: "The lesson of the referendum is we can no longer take anything for granted. And we know the struggle for equality is not over.
"If you want to change things, then join a union. Join other workers and win better rights, better public services and better working conditions. Individually we can only accomplish so much, but collectively we can move mountains. This wonderful celebration is proof of what we can achieve together."
The UK's major trade unions, including Unison and Unite, also backed a Remain vote at the referendum as well as Jeremy Corbyn and the Labour Party. But some Labour MPs, such as Frank Field, Gisela Stuart and John Mann, threw their support behind the Leave campaign alongside transport unions the RMT and Aslef.
Corbyn is expected to make a major speech on immigration, a top issue during the referendum campaign, in London on 25 June. An aide to the Labour leader told IBTimes UK that the left-winger would "definitely not" be announcing his intention to resign like David Cameron.
But Labour MPs Margaret Hodge and Ann Coffey have submitted a motion of no confidence in their leader. Corbyn's spokesman added: "We won't be addressing those particular MPs, but we will continue to talk about the real issues that now face people."