Union bosses are expected to set dates for national postal strikes which will cripple deliveries across the country and could cost the economy £1.5 billion.
The postal executive of the Communication Workers Union (CWU) will meet to discuss when to call out their members, following a huge vote in favour of industrial action.
It comes as the Centre for Economics and Business Research predicted that a week-long industrial action could cost the UK economy £1.5 billion, including a loss for online retailers of £220 million.
High street retailing, magazines and professional services will also be badly hit, while delays in receiving cheques could prove "fatal" to some firms, the centre's report warned.
In the event of a strike, one in four business mail items is likely to be sent by some other route incurring higher costs for business, it said.
The loss of a week's subscriptions for magazines alone would be £8 million, and the daily cost to the economy if a strike continued beyond a week was likely to be £300 million.
The CWU will decide whether to call out all 120,000 Royal Mail workers at once, or stage a series of strikes involving different groups of staff.
Dates for the action were due to be revealed on Monday, but no final decision was taken.
The union will have to give seven days' notice of a strike so the first strike could be as early as October 20.
Further talks with Royal Mail management are due to be held later this week but there is little sign of a breakthrough.
