It was meant to bring together the two of the largest teachers’ organisations to form a “super-union” that “politicians will have to listen to”.But the merger of the “radical” National Union of Teacher (NUT) with the more moderate Association of Teachers and Lecturers (ATL) has led to a bitter row, culminating in employees going on strike against their own union.The strike has been described as “highly embarrassing” for the newly formed National Education Union (NEU).”Intra-union strikes are very rare, it is almost unheard of for a union to organise a strike against another union. It it’s the worst possible start for the new union,” a source familiar with the dispute told The Sunday Telegraph.”Some ATL staff are concerned about the direction of the new union. Historically the ATL has always been very moderate. The National Union of Teachers, whose members were pictured here marching in April 2008, merged with the Association of Teachers and Lecturers Credit:ADRIAN DENNIS /AFP PHOTO ATL staff, many of whom are members of the GMB union, have complained that their pay and conditions will be worsened by the merger. A second motion signalled concern about the reputation of the new union as an “apolitical” group, and asked for guidelines to be produced on platform-sharing and affiliations with other organisations.A spokesperson for the National Education Union said: “There have been no resignations from the ATL section executive in protest at the amalgamation. “The number of individual member resignations from the ATL section has reduced significantly since the amalgamation.”There are always HR issues that arise with amalgamations as no organisation will have the exact terms and conditions of the other.”As a good employer, we are working very hard with the recognised unions to ensure the best possible outcomes for staff in the new union and discussions are continuing.” Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings. They voted nine to one in favour of strike action to take place at any point or continuously between this Thursday and December 31.Some staff have also launched a formal collective grievance against management over their handling of appeals. “It is very rich for a trade union to behave this way when it lectures everyone else about how to treat staff”, the source said.“The NUT staff are largely unaffected as this ‘merger’ is essentially a takeover.”Signs of inter-union strife were apparent at the ATL’s most recent annual conference, where members expressed their concern about the radical Left-wing causes that their NUT colleagues have long been associated with.One motion called for the new union to draw up “guidelines on funding and support for activities not directly related to education” and warned against engaging in activities “where the name and reputation of the union can be bought into questions”.It went on: “Many of the rallies, demonstrations and festivals supported by other unions may be close to the hearts and minds of a small proportion of our members without being something that a majority of the members would support or want their name or the name of the union attached to.” “There is quite a lot of disquiet as their members don’t want to be dragged into the militancy that has characterised the NUT. They fear that the hard Left will see the new union as a way in.”There was a strong element within NUT that was very engaged in anti-Israel stuff and my impression was that a lot of ATL feel uncomfortable about this.”The NUT has long exercised a formal boycott of Israel, and has previously been accused of “spreading political propaganda” in classrooms by teaching children and “extremist agenda” and promoting Palestinian “resistance”.