The Irish Medical Organisation has deferred a decision on whether to recommend the new public service pay agreement pending clarification on a number of issues.
Following a meeting of the IMO leadership, informed sources said the agreement as it currently stands would not be acceptable.
It is understood that the union will be writing to the Department of Public Expenditure and Reform and to the Minister for Health for clarification on issues.
The issues include lower pay rates for new entrants, the difficulties around recruitment and retention of doctors, and a number of outstanding awards.
Tomorrow the largest union, SIPTU, will decide whether to recommend acceptance of the extension to the Lansdowne Road Agreement.
Impact and the Prison Officers Association have already decided to recommend in favour of the deal.
However, the Teachers' Union of Ireland and the Irish National Teachers Organisation have decided to recommend rejection.
A number of unions are still considering their position on the draft agreement, while the Association of Garda Sergeants and Inspectors is taking legal advice on certain proposals.