A book of condolences is being launched for people to pay their respects to Mary Turner, long-standing president of the GMB union and member of the Labour Party's Executive, who has died after a short illness.
Labour leader Jeremy Corbyn led tributes to the former dinner lady, who went on to beceome one of the union movement's best-known figures.
Former GMB leader Paul Kenny described her as the most outstanding woman trade unionist of her generation.
Tim Roache, GMB general secretary, said: "Mary Turner has been the heart and soul of our union for a generation.
"The word 'giant' is sometimes overused, but in the case of Mary she really was a true giant of our movement. Mention the name Mary Turner and people will smile and say she had that unique blend of fighting spirit mixed with care and compassion.
"Be it fighting for dinner ladies in Brent, for hungry kids to have a free school lunch, for pensions, for young people, against discrimination and the National Front, Mary has led our movement. They broke the mould when they made Mary Turner."
Mr Corbyn said: "Mary was such a great campaigner for people. We first worked together in the early 1980s, defending school meals in Barnet, and I last saw her at a Labour National Executive meeting.
"She paved the way for so many women in the union movement and encouraged others to speak out."
The book of condolences will be opened online.