A disagreement over proposals in the Mental Health Bill to give responsibilities traditionally held by psychiatrists to 'registered clinicians', who could be nurses or social workers, has led to five organisations suspending their alliance membership.
Unison, Unite (formed by a merger of Amicus and the Transport and General Workers' Union), the Royal College of Nursing, the British Psychological Society and the College of Occupational Therapists have formed a breakaway coalition.
They want nurses and other qualified professionals to be able to extend or end community treatment orders. The Royal College of Psychiatrists supports the proposals in the bill.
Alliance chair Andy Bell said: 'We're disappointed but we accept that the organisations concerned want to focus their attentions on this issue.'
He stressed that there were still 75 organisations in the alliance.
But he also expressed his regrets at the breakaway coalition's decision, saying they could have just agreed to differ on the issue.
The two clusters agree on many other aspects of the bill, Mr Bell said.
But Unison head of nursing Gail Adams told HSJ: 'We feel we have taken our relationship with the alliance as far as we can.
'We all felt strongly about new ways of working within mental health services and the introduction of the registered clinician role.
'We need to be able to openly and actively articulate the concerns that our members and service users have expressed to us and we felt we would have been stifled if we'd continued with the alliance.'
The committee stage of the controversial bill has now ended and the legislation is expected to return to Parliament in early June for the report stage, when there will be a vote in the Commons.