The firm had applied to block the industrial action orchestrated by the Communication Workers Union after claiming it was "unlawful" because the union had failed to follow previously agreed upon dispute resolution procedures.
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 ballot is part of a flurry of union activity this autumn as public sector and health workers discuss the possibility of industrial action.
"We will now make contact with the CWU [Communications Workers Union] as a matter of urgency to begin the process of external mediation", Royal Mail said, adding that it remains committed of reaching a resolution.
"Our members are square behind the CWU and from this moment we are putting Royal Mail on notice of further action should the mediation fail".
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.
Royal Mail responded to the announcement by calling the action "illegal".
A spokesman from Royal Mail said the company had not yet heard from its lawyer.
General Secretary Dave Ward said: "The company are deluded if they believe their court room politics will resolve this dispute".
"Postal Workers" attitude towards the company will harden and it makes us more determined than ever.
CWU and Royal Mail have been embroiled in a dispute over the British postal company's plans to replace its defined benefit pension scheme, a move meant to prevent its annual contributions from ballooning to over 1 billion pounds by 2018.
'We are very committed to working closely with the union in order to reach agreement as a matter of priority'. "We must work together to save it", he said.