Last October, the NASUWT teaching union announced that it was in "formal dispute" with the Welsh government over a number of grievances, including workload and pay and conditions.
Since then, the union has spent a great deal of time trying to persuade ministers that its dispute is legal while insisting its members are "standing up for standards" in classrooms across Wales.
Last week, the union stepped up its campaign by vowing to take action against the introduction of a new performance management system, which it claims could lead to even more work for teachers.
It is particularly aggrieved that from September, teachers and headteachers in Wales will be required to keep a record of their work and the professional development they have received.
The union, which is strong west of the Severn, claims that the so-called Practice Review and Development (PRD) portfolio will be "workload intensive", "bureaucratically burdensome" and open to abuse by employers.
At the union's annual UK conference in Birmingham earlier this month, delegates voted for a "vigorous campaign" to secure additional funding for dedicated PRD time to be timetabled during teaching hours.
"Teachers already reflect on their work as a matter of course, but now the government wants to introduce a system to record that," Rex Phillips, the NASUWT Wales organiser, said. "We don't agree that it's necessary. The government hasn't assessed how this will impact on workload. We feel it's reasonable to ask for one lesson period a week to be set aside for this purpose."
However, a Welsh government spokesman insisted that education minister Leighton Andrews believes that teachers' performance is an important part of the process of improving results in the principality, which are lower than in the rest of the UK.
"Continuing professional development is at the heart of the minister's school improvement agenda. We in no way want to overburden teachers with additional workload, but it is imperative that standards improve for the benefit of learners in Wales," the spokesman said.
Mr Phillips said the union would review its national action instructions to protect teachers against the PRD portfolio if necessary.
Currently, NASUWT members in Wales are being instructed not to cover for absent colleagues, not to allow lesson observations outside performance management reviews and to allow only qualified teachers to observe them teaching.
These "actions short of strike action" form part of the union's trade dispute with the Welsh government.
Since January, the legality of the dispute has been argued in a series of back-and-forth letters between NASUWT general secretary Chris Keates and Mr Andrews.
"The Welsh government has asked the NASUWT to clarify on what basis it believes it has a legally based dispute with us. Discussions continue," the Welsh government said.
But Mr Phillips responded: "The Welsh government can say what it likes, but quite clearly we are in dispute and the education minister appears to be in denial of the fact."
He claimed that NASUWT members are regularly taking action, but could not give any details. The union has had no reports of its members being threatened with disciplinary action for making a stand, he added.
'A GREAT RESULT'
Christine Blower, general secretary of the NUT, congratulated the union's members in Wales for their successful campaign against an early years assessment system.
The Welsh government scrapped the controversial child development assessment profiles, a "snapshot" of the abilities of early years children, last month.
The NUT said they were time-consuming, ill-thought-through and denied children and teachers essential teaching time.
Speaking at the union's annual conference in Torquay over Easter, Ms Blower said: "This has been a great result for all the NUT teachers in Wales who have been campaigning on this issue, and most importantly will improve opportunities for children in school."
She called on the government to make sure that teachers were involved in any replacement scheme.