Mathe entered politics through SAMWU, an affiliate of the ANC-allied Congress of South African Trade Unions.
[3] In late 2015, the incumbent General Secretary, Walter Theledi, was suspended from his office amid allegations of financial mismanagement; SAMWU's executive committee voted in December 2015 to replace him with Mathe.
[8] More generally, Mathe presided over what the Mail & Guardian called a "leadership crisis" in the union, and in early 2019 the labour registrar applied to have SAMWU placed under administration for alleged violations of the Labour Relations Act.
[9][10] In April 2019, at a SAMWU executive committee meeting in Bloemfontein, five of the union's nine provincial branches supported a motion of no confidence in the incumbent national leadership.
[9] In the 2019 general election, which took place shortly after Mathe's removal from his SAMWU office, Mathe was elected to an ANC seat in the Limpopo Provincial Legislature, ranked 31st on the ANC's provincial party list.