The Irish Medical Organisation has said it is concerned with reports that the promise of free GP care at the point of access could be subject to a price for patients in the form of user charges.
It said it welcomed a European Commission report that prescription charges and co-payments are inequitable and inefficient.
Dr Ray Walley, chairperson of the IMO's GP committee, said that co-payments disproportionately penalise the sickest and most vulnerable groups.
He said GPs were being approached by patients constantly for advice on ceasing to take medicines on cost grounds.
Dr Walley said it was unacceptable that so many patients cannot afford to take all of the medicines they need and are asking what their most important medicines are and which ones they can do without.
The commission said that as a means of raising revenue, user charges are both inequitable and inefficient in comparison to pooled funding.
It said that as a means of moderating demand, they are constrained in that they do not have a selective effect between necessary and unnecessary treatment.
A spokesperson for Minister for Health Leo Varadkar said that when making submissions on government plans for free GP care, many GPs asked that there be co-payments, to discourage inappropriate visits to their surgeries.
He said that talks are ongoing with the Irish Medical Organisation and Minister Varadkar is to meet with unions in September and "will be happy to discuss it further."