The CWU threatened action before Christmas at what it perceives as unfair competition to Royal Mail from DSA providers - in spite of the fact Royal Mail has the freedom to set the access price it charges rivals for final mile delivery.

A ballot of CWU members representing some 160,000 Royal Mail employees, carried out this morning, returned a unanimous vote in favour of the threat of a mail boycott "if Ofcom fails to protect the UK's mail service".

It called for Ofcom to "immediately act in line with its statutory duty and intervene to protect the Universal service" and for minimum industry standards for postal workers (including DSA postal workers) "unerpinned by the Living Wage as a minimum for pay".

CWU deputy general secretary Dave Ward said: "This vote demonstrates the rising concerns among CWU members regarding changes to the postal service affecting jobs, services and performance standards.

"Competition in the postal sector is not benefitting the public - prices are going up and the regulator is actively consulting on reducing services from six days a week to five or perhaps even less."

However, a spokesman for regulator Ofcom strongly denied that it was consulting on reducing services: "We are analysing the needs of postal uses, so we've analysed how much people use and value six days a week, first class, that kind of thing and have invited stakeholders to comment on it. But we have absolutely no proposals to reduce the universal service from six days a week."

Ward went on to highlight the plight of small businesses, which he said relied on the universal service.

"Only big businesses with bulk mail contracts benefit from competition, yet we rarely see any evidence of them passing those price benefits onto their customers rather than just improving their own profits.

"Competition is being allowed on the basis of low-pay and unreliable job security in private companies. That will be a disaster for the sector if it continues. We will take this action to protect jobs and services if the regulator doesn't fulfil its duty."

The CWU has not yet released any details on how the proposed boycott - which DM printers have slammed as irresponsible and unrealistic - would work and has said it will publish further details in time for its annual conference in April.