Around 500 Communication Workers Union officials will hold a two-day policy forum in London from Wednesday to discuss a possible timetable for a ballot of 115,000 Royal Mail employees in the coming months.
Issues will include alternative business models to privatisation, pension changes and job security.
CWU general secretary Billy Hayes said: "UK postal services are facing unprecedented change and threats. We will always embrace innovation and changes in the industry, but only on terms which maintain decent jobs and protect quality services.
"This policy forum is all about anticipating what may lie around the corner and how CWU can react to protect the interests of our members and customers they serve in the increasingly changing world of postal services."
Deputy general secretary Dave Ward said: "We want to secure the best possible protections for our members' jobs and we will stop at nothing to ensure that their future, and that of the UK's postal services, are protected.