Unions have attacked the UK’s Royal Mail over plans to close its defined benefit (DB) scheme to future accrual, arguing the company should be careful not to present the closure as a foregone conclusion.

The Communication Workers Union (CWU), representing a majority of the postal service’s workforce, pledged to fight the plans to close the Royal Mail Pension Plan (RMPP), which reported a surplus at the end of March 2016.

Terry Pullinger, deputy secretary general of the union, said it was “unfortunate” the potential closure had leaked into the public domain, through a number of newspaper articles, prior to any formal consultation getting underway.

“The CWU do not accept that closure of the Royal Mail Pension Plan is inevitable and will explore every avenue to defend it,” he said.

Pullinger pledged to challenge what he regarded as conventional wisdom employed by employers, whereby sponsors de-risked by closing DB funds to future accrual.

“It is very concerning that the recent press articles, which have prompted this statement, give an impression of fait accompli,” he added.

“Royal Mail will need to bring far more imagination into these on-going discussions and should be in no doubt that the CWU will use every means at our disposal to encourage the company to think again and secure an agreement that defends our members incomes and dignity in retirement.”

RMPP is a multi-employer fund, which also acts as provider to workers within the Post Office, which is looking to close its section to future accrual.

Across both RMPP and its equivalent scheme for senior executives, Royal Mail reported an accounting surplus of £3.4bn – the result of the company’s privatisation, which saw the UK government take on a majority of the fund’s liabilities within an unfunded scheme.

The company has recently seen its pension contributions increase, with a £70m rise during the current financial year attributed to the end of contracting out of national insurance contributions in the wake of the UK state pension reform.