Unite general secretary Len McCluskey will join celebrations in Gibraltar tomorrow to mark the 40th anniversary of a historic week-long general strike.
The 1972 walkout ensured that public-sector workers in Gibraltar received the same pay and conditions as employees on mainland Britain.
Bosses had offered workers a derisory below-inflation pay rise of 40 pence.
But, backed by colleagues in the private sector, unions organised island-wide action and won a pay deal that was four times more than the original offer.
Mr McCluskey said that the trade unionists who took part in that landmark dispute ensured a fairer future for the island, which is known as "the Rock."
He said: "The trade union movement has a proud history in Gibraltar and today the unions continue to deliver justice and fairness to workers on the island regardless of nationality.
"It is right that we should pay tribute to the leaders and the workers who fought for fairness and justice.
"Forty years later Gibraltarians continue to enjoy many of the rights which the trade unions secured all those years ago."
Unite is the largest trade union in Gibraltar, representing workers in both the public and private sectors.
As part of his visit Mr McCluskey will meet Gibralta's chief minister and Gibraltar Socialist Labour Party leader Fabian Picardo.
Mr Picardo, who has led a coalition government since December 2011, has taken action to grant Gibraltan nationality to workers of Moroccan origin, who had been refused recognition by previous conservative administrations.