The local chamber of commerce is providing businesses in Drogheda, Co Louth, with a postal service to circumvent a dispute which has entered its fourth week.
The dispute is one of four causing disruption to mail deliveries in different parts of the country.
An Post is asking customers not to send mail to the two worst affected areas, Drogheda, and Tuam, Co Galway. There are also delays in the rest of Galway, both city and county, and in Mitchelstown, Co Cork.
Postmen in Drogheda said it is often not possible to deliver all mail within scheduled rosters, because of the growth in volumes to be delivered.
"Postmen were putting down as overtime the extra time spent delivering all the mail but were not being paid. Eventually they said if they weren't getting paid, they wouldn't do it," said Mr Brian Keenan of the Communication Workers' Union in Drogheda.
However, An Post said the dispute is unofficial and has appealed to staff to resume normal working arrangements.
It said it cannot pay overtime when it is not being worked and that any changes in overtime pay must be negotiated at a national and not a local level.
The company expects to lose €31 million this year. It said the overtime bill in Drogheda last year was €400,000.
"We were not able to pay the 3 per cent due under the Sustaining Progress national pay agreement because we could not afford it," a spokeswoman said. The company sealed all post boxes in Drogheda last month to prevent mail being posted. Advertisements were taken out advising customers to go to nearby towns to post mail.
The spokeswoman said this was to prevent mail from being "trapped" in the town. The company realised it was "hugely inconvenient to customers".
In response to the situation, the local chamber of commerce is accepting post from businesses in the town.
At the end of each day the mail collected is taken to another town for posting.
"Over 70 per cent of post from Drogheda is destined for outside the immediate area and we needed to protect the integrity of businesses here," said the chamber's president, Mr Mark Markey.
An Post said deliveries in the Drogheda area are currently one to two days behind schedule.
Deliveries in Tuam, where a dispute over staff accommodation is in its fifth week, are being delayed for about three days.
Following a one-day stoppage on February 3rd, staff have been refusing to work more than seven and a half hours a day in protest at the company's failure to find them new premises.
About half of the mail posted in other parts of Galway, including the city, is being delayed for about a day because of staff's refusal to allow post to be processed at the automated hub in Athlone. Instead, it is being sorted manually in Galway.
There is also minor disruption to deliveries in the Mitchelstown area because of a work-to-rule action.