The homeless charity Focus has appealed to management and unions at An Post to avoid a Christmas postal strike "at all costs".
Focus says a strike would seriously hamper its fundraising activities and cost the charity thousands of euros in lost donations.
Workers at An Post are planning a one-day strike on Wednesday in protest at the company's decision to close the SDS parcel delivery service.
But Focus fundraising manager Mr Mark Mellett said: "Another strike this Christmas would be a disaster. We appeal strongly to both sides to take whatever action is necessary to resolve this dispute without full scale strike action."
Mr Mellett said: "Charities like Focus Ireland depend heavily on the postal service. Christmas is a key time of year for our fundraising and we rely on people sending in donations by post in response to our advertising and appeals."
He added: "If there's another strike we will lose a lot of potential donations and despite people's desire to support our work, the fact is that some may then not be able to follow through after Christmas on their initial desire to donate money."