The National Ambulance Service Representative Association (NASRA) has said it cannot guarantee that patients will not be affected by their work-to-rule action in protest at the extension to the Croke Park Agreement.
The union which represents paramedics is to begin a series of actions today in protest over the cuts and changes to working hours.
Yesterday, SIPTU advised its 62,000 members to vote in favour of the new deal, but the NASRA insists the cuts are unfair.
Paramedic Michael Dixon said it was not their intention to disrupt patients, but that disruption could not be ruled out.
"It's impossible to give a 100% guarantee that people won't be affected," he said.