Wilson Sossion, secretary-general of the Kenya National Union of Teachers (Knut), has resigned.
Mr Sossion made the announcement at a press conference on Friday, saying he was frustrated by the government's failure to support his leadership.
His resignation came just a day before the union's national elections.
Boxed into a corner in the countdown to the national elections slated for Saturday, Mr Sossion had opened several war fronts with his opponents and government institutions.
He had picked a fight with Knut’s acting national chairman, Mr Collins Oyuu, who was to face off with him for the secretary- general’s position in what had narrowed down to a two-horse race.
He had also accused the Labour ministry of “dishonesty, and outright biasness in planning and supervision of the election,” and had alleged that the union was considering appointing the Independent Electoral and Boundaries Commission (IEBC) to preside over the polls.
The union has also been having frosty relations with the Teachers Service Commission (TSC).