The company said the proposed deal would increase base rates by 8.6%, with a lump sum of £300 in December 2013, adding that it wanted a "new model" for the company to work together with the Communication Workers Union (CWU).
But the union rejected the proposal, branding it "misleading and unacceptable". The CWU and the Unite union will lobby MPs in Parliament as part of their campaign of opposition to the planned sell-off of the Royal Mail.
CWU deputy general secretary Dave Ward said: "Postal workers want more security; what's on offer is less. With privatisation looming, the protections Royal Mail have put on offer are not worth the paper they're written on. Our members clearly voted - by a huge 99% - for a pay rise without strings attached, yet the company ignores them."
Mr Ward said the Government and Royal Mail chief executive Moya Greene had promised a year ago that postal workers' pensions were safe, adding: "Now they have reneged on their promise and postal workers' pensions are again under attack.
"The pay rise is only there as a sweetener to swallow some very bitter pills on damaging changes to pensions, and a raft of workplace uncertainty. The deal that they've spun in their press release is not the real deal. Postal workers will know that. If we can't get the assurance we want over our members' future, then industrial conflict is inevitable."
Ms Greene said: "Co-operation is central to the future success of the company. This offer represents Royal Mail's commitment to a long-term engagement strategy with the CWU and with our people. We have already built a stronger Royal Mail together through closer co-operation and trust in recent years. We are now offering a new long-term agreement with the CWU and our employees.
"This is a good deal - good for Royal Mail and good for our people. We are asking the CWU and our people to accept this new agreement. There will be further discussions this week with the CWU about the proposed agreement."
Unite officer Brian Scott said: "Our postal service doesn't need privatisation. Its annual profits show that it is able to succeed in public ownership. Our Royal Mail management members are becoming increasingly concerned about the proposed privatisation and its implications for the public, pensioners, the disabled and small companies, as well as future employment and their pension provisions."