Staff at the Passport Office have served protective strike notice on the Government, which could take effect in seven days.
Sources in the Civil Public and Services Union said the move was triggered by the Department of Foreign Affairs' threat to dock employees' pay if they refused to carry out their duties.
However, they stressed strike action would only take place if the Government deducted pay from their members.
The move comes as talks on public sector pay and reform are due to enter an intensive phase over the weekend.
Some sources speculated the CPSU move could be intended to leave them the option of taking strike action in the event that those intensive talks breakdown.
The Irish Travel Agents Association said the CPSU action was ‘calculated to make life as difficult as possible’ for people seeking travel documents.
Chief Executive of the ITAA Simon Nugent appealed to the CPSU to suspend its industrial action as the Government now knows ‘they're able to throw a bomb into the middle of the passport system’.
He said there is a rising level of panic, which cannot be tackled without the unions’ cooperation.
Department of Foreign Affairs Secretary General David Cooney this morning appeared before the Foreign Affairs Committee in the Oireachtas to discuss the crisis.
Mr Cooney apologised to customers and said he found the current situation personally very upsetting.
He said the Department wants a cessation of industrial action, including non-cooperation with temporary staff, as well as the lifting of bans on overtime and the answering of phones.
The backlog is now so large that all applications are urgent, he said.
Fine Gael TD Alan Shatter told Mr Cooney that a letter should be sent to the unions saying they would be added to any compensation claims arising from the industrial action in the Passport Office.
Assistant Secretary General at the Department of Foreign Affairs Ray Bassett brought up the issue of privatising the production of passports.
Mr Cooney said the outsourcing option is there, but it cannot be achieved overnight.
The best thing is for the industrial action to end and for the needs of the people to take priority, he said.
Mr Cooney also agreed with Assistant General Secretary of CPSU Theresa Dwyer that the closure of counters is not the problem, it is the cumulative effect of several weeks of industrial action.
Head of the Passport Service, Joe Nugent, said the situation at the Passport Office this morning was very ugly.
He said that the CPSU's promise last night to amend its industrial action contributed to this situation.
Yesterday, it was announced that staff would give priority to those with immediate travel plans.
Earlier today, a Co Wicklow man chained himself to internal doors in the office.
The man accepted an assurance that he will get his passport on Friday and has now left the building.
The queue at the office has greatly reduced and there are now about 70 people outside the building, compared to hundreds this morning.
Further information is available on www.passport.ie
