As the primary union for approximately 130,000 Royal Mail workers, the CWU is opposing moves to transfer the service away from full state ownership.
Two months ago Royal Mail called in City PR agencies Brunswick and Tulchan Communications, to lead it through a privatisation process (PRWeek, 8 February).
The launch partners for Save Our Royal Mail include the Countryside Alliance, the National Pensioners Convention and the Scottish Family Business Association.
Royal National Institute for the Blind vice-president Lord Lowe is also involved.
The campaign links the possible impact of a Royal Mail sell-off to six areas of concern: stamp prices; rural services; small businesses; Royal Mail's heritage; Freepost services for blind people; and Freepost services for HM Forces serving overseas.
The campaign is directed by PSA's associate partner Mario Dunn, who was a special adviser to Labour minister Alan Johnson for five years until 2010. Johnson was a postman before becoming leader of the CWU in the 1990s.
Agency founder Philip Snape said: 'We came up with an idea to create a coalition to protect postal services, part of which was pulling together a diverse group of organisations with a shared interest in this area.'