The Communications Workers Union has accused An Post of sabotaging the postal service and says it is concerned that 10,000 An Post's workers will not be paid next week because of the suspension of delivery services.
CWU General Secretary Steve Fitzpatrick said the company has made clear to him that if there is no mail to deliver on Monday workers will be sent home and that he expects they would not be paid.
He said as 40% of mail is sorted manually there was no need for a total suspension of the service.
But the company at the centre of the dispute, IO Systems, has accused the union of bringing the postal services to halt.
IO Systems Managing Director Fergal Lynam said that since just after midnight on Friday management at his company, An Post and the machinery manufacturers had been maintaining the sorting machines and that they remain ready to operate.
But he said the CWU instructed its members not to operate the machines.
The union denies this.
Mr Lynam says the issue has nothing to do with An Post and relates to a cut in shift premiums rather than gross pay which effects 25 of its 36 employees.
It says the change stems from the fact that An Post no longer need the technicians to work weekends and they therefore changed their roster from a seven-day twelve-hour shift to a five-day eight-hour shift.
He said the majority of workers lost between 6-9% of their premium and that just three of the 25 had experienced 22% cuts as had been claimed by the union
He said the technicians involved earn between €70,000 and €100,000 each and are therefore among the highest paid technicians in the country and that the shift premiums they receive are also among the highest.
He said the company is willing to engage with the Labour Court or any other third party and to agree to a binding resolution on the matter.
Meanwhile, a major online retailer has said that if the dispute continues for much longer it could do serious damage to his business.
Michael Lynam of car part retailer micksgarage.com said the suspension of services has been a "bombshell" for his business as up to 98% of their deliveries are made through An Post.
He said his business was built on next day delivery and that being unable to do this could result in a loss of customers.
The Irish Postmasters Union has said the industrial action has put its member's livelihoods at risk.
General Secretary Ned O'Hara said he was surprised that in 2015 the postal service had been suspended due to industrial action and that the issues could not be resolved around the table
He said the IPU have been fighting for more and better services to be provided by An Post and that this would now damage the relationship with business and encourage them to go elsewhere.
