As he rose up the ranks to the top of the SNTE, she rose with him.

BBC: 'La Maestra' of Mexico faces her biggest challenge

Mr Diaz told the SNTE congress in Guadalajara that the way his union had been sidelined over the recent education reforms was a crime.

BBC: Mexico union replaces Elba Esther Gordillo

Ms Gordillo, who has led the SNTE for the past 23 years, and who was elected unopposed to another six-year term in October, was not present at Monday's signing ceremony.

BBC: Mexico's Pena Nieto enacts major education reform

Until now, the National Union of Education Workers (SNTE) has held sway over the criteria for being appointed and retained, a practice that has led to posts being inherited or sold.

BBC: Mexico's Pena Nieto enacts major education reform