The Labour Party and SDLP have described a decision by the Association of Garda Sergeants and Inspectors to withdraw co-operation from the North/South policing protocol as regrettable.
The protocol would allow gardaí to be seconded to the PSNI in the North and PSNI officers would be cleared to work in the Republic.
Garda Commissioner Noel Conroy and the Police Service of Northern Ireland Chief Constable Hugh Orde signed the joint protocols last month.
However, at its annual conference in Kilkenny, the AGSI voted not to participate today, citing concerns for the safety of gardaí and the costs of such co-operation.
Labour justice spokesman Joe Costello said the move could be seized upon by opponents of the PSNI and those opposed to the Patten reforms of that force.
SDLP policing spokesman Alex Attwood said he would seek a meeting with the AGSI to "convince them of the folly of their approach".
Mr Costello said: "At a time when events such as the Northern Bank robbery and the subsequent cross-border investigations and raids arising from this case have demonstrated the importance of Garda/PSNI co-operation, I find it baffling that the AGSI decide to withdraw support for a scheme that has already been legislated for and agreed between authorities North and South."
Mr Attwood claimed the AGSI were "turning their back on a good way to get better policing results to the benefit of all the citizens on the island".
The idea for exchanges and secondments was first recommended in the Patten Report on the future of policing in Northern Ireland in 1999.
The British and Irish governments carried forward the idea in an inter-governmental agreement on policing they signed in 2002. Under that agreement, the two police services have devised the protocols that now facilitate the movement of officers between their forces.
