Postal services to rural areas face delays of up to two hours on the third day of the pay dispute between the Irish Postmasters' Union (IPU) and An Post.
The 600 members of the IPU contracted to run rural post offices are refusing to accept deliveries from central locations until 8 a.m. - two hours later then usual. Postmasters are also refusing to supervise and assist mail-sorting.
An IPU spokesman said there would be an accumulation of undelivered post at centres across the State, causing delays of up to one-and-a-half days.
This was rejected by a spokesman for An Post, who said it was an "absolute nonsense" to suggest there would be a significant backlog by the end of the week.
The dispute centres on pay and conditions for the contracted postmasters. Postmasters have been paid €2 an hour for supervising and assisting with mail-sorting. Their union is looking for a €40 per hour increase for sorting duties and for post offices opening before 8 a.m.
But An Post said the contracted postmasters have already received significant pay increases over the past five years.
No further talks are planned between the two parties.