Members of the RMT Union will begin voting for a new General Secretary today. The new boss of the National Union of Rail Maritime and Transport Workers will replace Bob Crow who died of a heart attack in March after 12 years in the job.
The ballot will remain open for the next two months.
The Rail, Maritime and Transport union said Mr Crow's family have asked for the funeral service at the City of London Cemetery and Crematorium to be private but have invited trade unionists, friends and colleagues of Mr Crow to line the route of the funeral procession.
The procession will include trade union banners and flags and will end at the cemetery gates.
But the RMT executive said it hoped for a huge turnout at the annual May Day march in London to honour Mr Crow, who died earlier this month at the age of 52.
Mick Cash, the RMT's senior assistant general secretary, said Mr Crow's death had rocked the trade union movement, both in this country and around the world.
As members of the Rail Maritime and Transport Union voted to strike, the union warned further action would be taken if the row is now resolved. Workers on the Piccadilly Line will walk out for 24 hours on 4 December, but didn't rule out a 48 hour strike at a later date.
RMT general secretary Bob Crow said:
"The overwhelming 88% vote in favour of strike action can leave management in no doubt that the union is not prepared to accept the continuing abuse of individual drivers and negotiated agreements on the Piccadilly Line."
Workers on a busy London Underground line are to strike in a row over agreements being "ripped up". Members of the Rail Maritime and Transport union on the Piccadilly Line will walk out for 24 hours from noon on December 4.
"The outcome of these separate ballots will now be considered by RMT's executive but the message could not be clearer - we are stepping up the fight to protect agreements, jobs and working conditions across the whole of London and to eliminate the scourge of poverty pay on cleaning contracts."