Postal deliveries in rural areas face a fourth day of disruption over a pay dispute between the Irish Postmasters' Union (IPU) and An Post.
More than 600 members of the IPU contracted to run rural post offices are refusing to accept deliveries until 8 a.m. - two hours later then usual. They are also refusing to supervise and assist mail-sorting.
An IPU spokesman said undelivered post would accumulate causing delays of up to one-and-a-half days.
A spokesman for An Post rejected this suggestion as "absolute nonsense".
The dispute centres on conditions and pay for the contracted postmasters.
The IPU is looking for a €40 per hour increase for sorting duties and for post offices opening before 8 a.m.
Up to now, postmasters have been paid €2 an hour for supervising and assisting with mail-sorting.
An Post said the contracted postmasters have already received significant pay increases over the past five years.