Angry teachers unhappy at how the General Teaching Council for Wales (GTCW) conducts disciplinary matters want the body to be scrapped.
Staff called for the council to be abolished at the Welsh-medium teaching union UCAC's annual conference, which began today.
Gruff Hughes, general secretary of the union, said there were widespread concerns that the teaching council's regulatory role had become too "heavy handed".
The union said teachers now see the GTCW as a body that impeaches teachers, not one that protects the profession. "The majority see it as a body that disciplines teachers," said Mr Hughes.
"One member has been investigated five times by different bodies - including the school, the governors and the local authority. It's been going on two years. It's like our members are going on trial."
Other teacher unions have also voiced similar concerns.
Rex Phillips, regional organiser of the NASUWT Cymru, wants the teaching council reformed without lay members so that teachers would be regulated by their peers. He said some were being subjected to "quadruple jeopardy" by the body.
"It could deter people coming into the profession," he said. "I'd prefer all hearings to be held in private with the outcomes made public."
Tim Cox, a national executive member of NASUWT Cymru, said while legislation requires the council to benefit the public rather than teachers, "things had gone beyond what the public would expect". "By bringing some cases, it actually puts the profession into disrepute," he said.
Mr Cox, appointed to the GTCW as a union rep by the Welsh Assembly government, said there was still widespread anger within his union that the teachers' annual registration fee had risen from pound;33 to pound;45 and is no longer fully subsidised by the Assembly government.
"We're having to pay for expansion of the GTCW's disciplinary process - they say hearings are more expensive and there's more than they planned for," he said. "We think they should speed things up by doing things like plea bargaining."
Earlier this year, the teaching council was condemned by the National Association of Head Teachers Cymru (NAHT) for the way it handled the case of Paul Davies, the former head of Cwmdare Primary, near Aberdare.
Mr Davies was struck off at a council disciplinary hearing in February after he caused a road crash that left one man wheelchair-bound and unable to work.
The former head had already received a 15-month prison sentence for dangerous driving. Now he is to appeal against the GTCW's verdict at the High Court in London next month.
Mr Davies is being backed by the NAHT Cymru. Anne Hovey, a regional adviser for the union, condemned the council for being excessively harsh. "He had an unblemished record professionally," she said. "Matters to do with people's actions in their private lives that have no direct connection with their suitability to teach are coming into play, and they shouldn't be."
But Mal Davies, GTCW chairman and head of Willows High in Cardiff, defended the teaching council's record. "This is the first case from a hearing that's been challenged in the High Court, so we haven't made too many mistakes," he said.
"An investigating committee sees whether there's a case to answer. Do we want to be a grown-up profession regulating ourselves, or have civil servants doing it?"
Dr Philip Dixon, director of the Association of Teachers and Lecturers in Wales, also backed the GTCW. "It's provided a great service in re-professionalising the workforce," he said.
"I think hearings need to be held in public. Behind closed doors they could lose an element of public confidence."
Gary Brace, the GTCW's chief executive, declined to answer questions from TES Cymru, but through a PR firm's statement he said its procedures were part of its statutory responsibility.
"The council aims to maintain and improve standards of professional conduct," it said. "One way is to ensure allegations of incompetence or misconduct are thoroughly investigated and appropriate action taken to protect public confidence.
"We only investigate cases referred by third parties, such as education authorities, employers and the police. Of referrals received since 2001, the council has closed around 80 per cent of cases because they had no merit or were vexatious."