The CWU said it had "no alternative" but to stage a 24-hour walkout on July 13, following on from the industrial action it took on June 29, after management did not improve its 2.5% pay offer and disputes over modernisation of the business continued.
According to the CWU, around 95% of its 130,000 members took industrial action in last month's strike, and the second next week will cause severe disruption to business mail services across the UK. Royal Mail has disputed the figures, claiming turnout was closer to 60%
In a letter to Allan Leighton, chairman of Royal Mail, CWU restated its reasons for taking industrial action, and asked for "meaningful negotiations" about modernising the company, raising the value and status of postal workers, and making the business more competitive.
Dave Ward, deputy general secretary of the CWU, stated in the letter that Royal Mail's "public refusal to engage in fresh negotiations leaves the union no alternative other than to announce further strike action". The union said strike action could be avoided if "immediate negotiations" were held.
Ward warned that Royal Mail restating its position would not be enough to avert next Friday's strike.
The CWU has raised concerns about Royal Mail's methods of modernising and claims that the relocation of post office branches into retailer WH Smith would close 85 post offices and result in 40,000 job losses.
In a response, Royal Mail said it did "nothing but continue to offer talks to re-explain their position. It is important to understand [we] are not offering negotiation, we are in the middle of a dispute and only a negotiated settlement is the solution to this dispute".