Deficit in Royal Mail pensions
Royal Mail said its senior executives' pension plan had a "significant" deficit and the company was legally obliged to make payments into it.
The Sunday Times said Royal Mail has set aside £90m for the scheme while it was asking other employees to accept reduced benefits.
Pensions is one of the issues which could trigger a strike ballot among over 115,000 CWU members soon.
The company said in a statement: "The Royal Mail Senior Executives Pension Plan closed to new members in 2008. It closed to existing members in 2012.
"It was not included in the pension transfer to Government in April 2012.
"Based on the most recent actuarial valuation, RMSEPP had a significant deficit and the company is legally-obliged to make payments towards it.
"The company has a proposal to keep its main plan, the Royal Mail Pension Plan, open to future accrual, subject to certain conditions, without increasing members' contributions, retirement age or rate of accrual."