Workers at An Post have voted overwhelmingly in favour of industrial action.
The ballot of Communications Workers Union members - some 8,000 staff - was called as part of a pay dispute and union officials have already said they expect a sizeable majority to back the strike plans.
The staff voted by an 89.7% majority in favour of the move. The strike is due to get underway in two weeks time.
An Post had offered the CWU a gradual 9.5% pay increase, as well as 15% of the company as part of a profit-sharing scheme.
However, the union said these are merely allowances and will not be pensionable or reckonable for sick pay and holiday pay.