Four ESB workers are to begin a legal action against their employer within weeks over the payment by the company of a dividend to the Government.
Solicitors for Brian Baitson, William Flavin, Owen Kilmurray and Margaret O'Connor have written to the ESB.
They claim that the payment of a €78m dividend and €400m from the sale of company assets is unlawful due to a €1.7bn deficit in the pension fund.
They said the deficit needs to be addressed as a matter of priority.
The ESB has rejected the claim and said that the pension fund is not in deficit, according to the scheme's actuary.
It also said it has no liability to address deficits in its pension fund.
The four plaintiffs claim that the ESB's designation of the pension scheme as a defined contribution, rather than defined benefit-type scheme in its annual report and accounts, is not accurate.
The ESB also rejects this and in a statement to RTÉ said: "ESB's financial statements fully and accurately reflect ESB's obligations to the scheme.
"The financial statements are in compliance with all relevant accounting standards, and have been approved by the company, its audit committee and board. All of ESB's audit opinions have been unqualified.
"The accounting treatment of the scheme does not affect the rules of the scheme or members' benefits in any way."
The ESB Group of Unions said the company's statement was not correct.
It said: "ESB has the same obligations to fund deficits that it has had since 1942. There is no change.
"Changes in the ESB accounts and statements since 2011 in relation to their pension liabilities are without agreement and baseless."