Ms Caden, a prominent former EIS president, has accused the union of "pettiness". She said: "I feel there is a bit of a personal vendetta against me because I have not been active in the union recently or been seen to be active."
All teaching unions traditionally support a "slate" of official candidates in the four-yearly elections to the GTC, in a bid to influence the vote for the 22 primary and secondary teacher seats on the council. But Ms Caden, the most high-profile casualty of that system, says she is ignoring the normal appeal by the union to abide by a collective decision and not to stand against official candidates.
Ian McKay, EIS assistant secretary, wrote to Ms Caden that the union "has sought to find a balanced list which takes account of a number of important criteria, including professional experience, EIS involvement, geographical spread, gender, demographic considerations and the continuing need to promote the involvement of new personnel".
Mr McKay said: "The same criteria were applied when Ms Caden was a candidate at the last GTC elections and at the elections before that, and they apply to everyone. It is unfortunate that people are prepared to abide by the rules when they are selected and ignore them when they are not, but that is a matter for their individual consciences."
Mr McKay's letter to Ms Caden stated that "a number of otherwise excellent candidates" had to be rejected to produce a balanced list. Ms Caden said she "has yet to find a second one".
The TESS understands, however, that one other EIS-supported member of the current GTC failed to be endorsed and three others withdrew anticipating that the union's selection criteria would work against them. None is planning to stand against the official candidates.
Mr McKay denied Ms Caden's claim that she was being penalised for putting her GTC work before that of the EIS. One other former union president, Wolseley Brown, still enjoys EIS backing. He is a leading GTC member and chair of its committee on exceptional admissions to the register. May Ferries, a more recent EIS president, is also on the election slate. Mr Brown and Ms Ferries are both west of Scotland primary teachers. Ms Caden teaches in an Edinburgh secondary.
The EIS traditionally dominates the primary elections, but faces a tougher battle for secondary seats against the Scottish Secondary Teachers' Association.