A planned strike involving Northern Ireland postal workers would be " extremely concerning" for local businesses, it has been warned.
Last-gasp talks between union leaders and the Royal Mail aimed at averting action continued this morning.
But up to 130,000 members of the Communication Workers Union (CWU) across the UK were set to walk out at noon today for 48 hours and again on Monday in a row over jobs, pay and pensions.
Glyn Roberts from the Federation of Small Businesses said there was "no doubt" that such a move would disrupt businesses in Northern Ireland.
"Survey after survey that the FSB has done has shown that nearly 90% of all business rely on Royal Mail for vitally important things such as cheques and invoices," he said.
"It does affect cash flow of any small business, and it does get more serious for a business that does rely on the mail such as mail order companies.
"It is extremely concerning that the economy will face disruption.
"It wasn't that long ago that we had a month-long strike here which brought many businesses almost to their knees. Some businesses saw an almost 90% reduction in their cash flow. Many of them struggled.
"The message to both sides would be to stick at the negotiating and try and get a deal.
"I think it's very important that both sides go the extra mile."
Meanwhile, Royal Mail said it will do "all it can" to mitigate the impact of any action, but that a strike would " severely limit" its ability to provide anything but a skeleton service.
"Customers should expect severe disruption to all postal services and our advice is not to post mail on the strike days," said a spokesman.
"If it is absolutely necessary, then please do so at one of our Post Office branches, all of which are operating as normal.
"Up to date information is available on our website: www.royalmail.com or by calling our customer helpline on 08457 740 740."
Union leaders have warned that a rolling programme of strikes will start on October 15 and will continue every week until the dispute is resolved.
Dave Ward, the union's deputy general secretary, said that despite several weeks of negotiations, Royal Mail had not taken on board the union's message that the company needed to invest in the workforce.
"The workforce has had enough of Royal Mail messing them around," he said.
" We're not going to tolerate an employer that ignores its workforce, ignores the union and ignores its customers."
Postal workers have staged four national strikes and other forms of industrial action since the summer after rejecting a 2.5% pay offer and the Royal Mail's modernisation plans, which the union claimed would cost 40,000 jobs.