Train drivers' union leader Shaun Brady has been sacked for "gross misconduct", following a disciplinary hearing of the Aslef union's executive.
Shaun Brady says he is "extremely disappointed and bewildered"
The decision is thought to relate to his failure to co-operate with an independent investigation into alleged financial irregularities.
Mr Brady still faces other internal matters concerning a fight with another union official at a barbecue.
This will not be dealt with until next week. He has six weeks to appeal.
An appeals committee made up of representatives from eight Aslef regions
would then be set up, and its decision would be binding.
At Thursday's hearing, each of the seven executive members put a separate disciplinary charge to Mr Brady.
He was cleared of deliberately attempting to mislead QC Matthias
Kelly QC's investigation into alleged financial irregularities.
The executive also accepted his explanation for the alleged use of an Aslef credit card to obtain a
£6,228.13 cash advance.
And three other charges, including one of bringing the union into disrepute,
were deferred because witnesses had not turned up at the disciplinary hearing.
But on Friday, a letter was sent to Mr Brady's Southampton home by courier informing him of his dismissal.
The 41-year-old told the BBC News he was "extremely disappointed and bewildered" by the decision.
Mr Brady was suspended in May, along with assistant general secretary Mick Blackburn and president Martin Samways, five days after a fracas at a barbecue held at the union's head office in north
Mr Samways later resigned. Mr Blackburn faces a disciplinary hearing next week.
In June, Mr Kelly's report accused Mr Brady of handling the union's staff "aggressively
It said he had engaged in a power struggle and urged the union to stamp out a "self-destructive culture".
The union's annual conference was then suspended, and has been rescheduled for September.
Mr Brady is the first serving union general secretary to be sacked since 1991, when the National Union of Journalists' leader was dismissed after clashing
with his executive.
Former South West Trains Mr Brady driver has been at odds with his executive since his surprise election victory over left winger Mick Rix last year.
Mr Brady took office in October but has since been involved in a series of
clashes with the union's leadership and staff.
He said the executive had stripped him of power, and he had to ask permission to buy a jar of
And the TUC had to intervene to broker a deal between Mr Brady and the GMB union, which
represents Aslef employees, after he threatened some head office staff with dismissal.