Of those who voted, 89.1 per cent cast their ballot in favour of strike action.
Royal Mail, which was privatised four years ago, argued the CWU had missed a Monday deadline to remove the threat and agree to peace talks. "The first step is selecting a mediator acceptable to Royal Mail and the CWU from a panel that was agreed by both parties under the Agenda for Growth".
The court action is the latest twist in a bitter row between the union and Royal Mail.
The CWU says its list of gripes with the company are all linked to the privatisation - accusing bosses of cost cutting and asset stripping to satisfy shareholders.
But CWU deputy general secretary Terry Pullinger slammed Royal Mail for "playing politics" rather than engaging with the union to reach an agreement.
"Any sense of vocational spirit and working together with management has been lost in a climate of fear and insecurity".
"The managerial leadership has failed and should resign or be sacked".
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The postal services company said the United Kingdom higher court has ruled that contractual dispute resolution procedures under the Agenda for Growth must be followed before industrial action can take place.
The company said it remained committed to finding a deal on pensions and pay, with offers still on the table including wage increases of 5% - linked to productivity improvements.
The mass walkout - the first planned by workers at the company since it was privatised - could now be pushed back by at least nine weeks. It undermines the trust of our customers. It provides protection to employees and stability to the company.
But the High Court today sided with Royal Mail's contention that the proposed industrial action was in breach of a side agreement mandating further actions must first take place.
The company also pointed out that a strike would be self-defeating for staff as they owned a fifth of Royal Mail shares.
Update: 17:50: Here's a video from Royal Mail explains that it's business as usual as negotiations continue.
The company has written to the CWU invoking a "legally binding external mediation process", and reiterating that any industrial action would be unlawful.