IMPACT this morning instructed its members not to carry out work which pertains to the 169 posts due to be cut by the Western Health Board.
In an escalation of its dispute with the health board, the union is also to consider withdrawing from partnership structures when it meets with board officials on Friday.
The Western Health Board claims it is being forced to cut up to 200 jobs to meet a Department of Health demand to save €1.15 million.
The Minister for Health and Children, Mr Martin, angrily rejected this level of job cuts were required, saying the savings could be met by the non-filling of 85 sanctioned posts.
SIPTU and IMPACT have said they will strongly resist any job cuts in the Western Health Board.
A number of temporary staff have already received letters informing them that their contracts would not be renewed, according to IMPACT. The union had requested that no job losses be imposed until the consultation process has been exhausted.
Mr Kevin Callinan, IMPACT National Secretary said the job cuts mean health professionals will spend more time on clerical work and less time treating patients.
The Western Health Board has refused to comment on suggestions that it employed 320 people more than it had received sanction for in 2001.
Mr Callinan called on the Minister for Health to rethink the 800 health cuts, adding that the Department's calculations of what can be saved are wrong.