Last week, 89% of the CWU's 111,000 workers backed a walkout in a dispute over pensions, pay and jobs, with 74% of members turning out to vote.
Royal Mail PLC on Thursday secured a court injunction over a potential industrial action announced by a union representing its employees.
As previously reported, the CWU members have voted for industrial action, with a 48-hour walkout scheduled to start on 19 October.
It claims that an injunction is appropriate to prevent the deliberate inconveniencing of hundreds of thousands of people across the United Kingdom, as well as commercial loss to the company.
In response, the union tweeted: "Royal Mail won the injunction but we stand here with 90% yes vote and more strike action ready to come".
Royal Mail, which was privatised in 2013, is trying to modernise after years of underinvestment and has reduced layers of management, upgraded technology and cut its property bill. The last mass industrial action among postal workers was in 2009.
"But sooner rather than later Royal Mail Group will have to confront the harsh reality that they are completely out of touch with the views of its workforce", CWU General Secretary Dave Ward said.
However, Royal Mail has argued that it would be illegal for the CWU to coordinate a strike until the contractual external mediation process has been followed.
Royal Mail said talks would likely take until around Christmas time to complete, or possibly longer. 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.
Mr Justice Supperstone, who made the ruling, said: "I consider the strike call to be unlawful and the defendant is obliged to withdraw its strike call until the external mediation process has been exhausted".