A Lloyds Bank union is taking legal action to close the pay gap between men and women who took out guaranteed minimum pensions (GMPs).
Lloyds Trade Union (LTU) hopes the case, which will be brought on the grounds that "sex discrimination is unlawful", will remove a £2,000 per year gap in the company's defined benefit (DB) schemes.
It affects women who took out GMPs between 1978 and 1997, substituting their state pension for a higher private pension. However, GMPs were calculated on the basis women received their state pension five years earlier than men, at age 60.
The LTU calculated the total cost of equalising payments for more than 100,000 affected women would be around £300m, excluding legal and administration costs.
The union undertook legal advice, which concluded pensions were considered deferred pay, and therefore need to be equalised. The case is expected to be heard by an employment tribunal. It is not yet known when that will take place.
Lloyds declined to comment.
Irwin Mitchell head of pensions Martin Jenkins said the case, if successful, could force other companies to undertake GMP equalisation.
He said: "The case has the potential to bust the issue wide open. Almost all DB schemes are affected by the issue and the vast majority have got the thing locked away in a bottom drawer in the hope they never have to tackle it. This has the opportunity to bring it to a head.
"This case has significant merit. I would imagine an awful lot of other schemes would find they have a similar issue."
The case could also act as a catalyst for similar action in other UK companies, potentially costing the industry more than £13bn.
Jenkins added: "It's not an unrealistic estimate if you think GMPs are a big trance of benefits and a large slice of the cake for that period [1978-1997]. The figure seems to be a credible estimate of the impact it could have across the industry. It's one for the industry to worry about."
The issue of equalising GMPs has caused headaches for the industry, after a 1990 judgement by the European Court of Justice (ECJ) said the retirement date for benefits should be the same for men and women.
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