The spokesperson added that the company was also seeking talks with the CWU at dispute resolution service Acas.
It is possible that the decision to terminate the agreements with the CWU could be challenged in court, an insider acknowledged.
But they added: “You couldn’t paint a clearer picture of industrial instability. The case is quite clear.
Dave Ward, CWU general secretary, previously brushed off the threat to drop the deal.
The union is demanding a pay rise for staff to at least match inflation and has pushed back changes to rotations that would see postal workers deliver parcels later in the day.
Mr Ward said the union was ‘ready for this fight and we are confident the public will support us’.
“Royal Mail wants to change the whole basis of what the business is,” he previously told The Telegraph.
“The council’s proposals will make it just another parcel courier – it’s about ditching the universal service obligation and making as much profit as possible.
“We think they are taking liberties, not only with our members but also with the public, and that is why we are on strike.”
Royal Mail’s deal with the CWU was signed under former chief executive Moya Greene in December 2013 as the company sought stability after a bumpy stock market debut in October. It was advertised as “groundbreaking…the first of its kind in the UK”, with the company claiming it would “create a culture of can-do”.
But current management, led by executive chairman Keith Williams, sees the contract as an obstacle to making changes essential to the company’s survival in the modern age.
Royal Mail is struggling with a sharply declining letter market, but demand for parcels is soaring, propelling the growth of rivals such as Evri, DPD and Amazon. Bosses say the company’s network of local sorting offices and unreformed labor practices prevent it from competing on a level playing field.
They have tried to set up new parcel delivery hubs and want postal workers to deliver later in the evening and on Sundays, but have faced strong resistance from the CWU, which believes the changes undermine the role of its members.