The company, a major defence contractor for the Ministry of Defence that also has operations in the nuclear sector and other areas, said the cost of the scheme has risen significantly and unexpectedly since it was last reformed in October 2014.

Babcock International is proposing to increase the member contribution rate from 6% to 9% from October 2017 and to 12% in October 2017.

Neil Walsh, Prospect’s pension officer said: “Scheme members are extremely disappointed that the reforms implemented less than three years ago have to be revisited so soon afterwards.

“Prospect has only been provided with headline figures from the latest scheme valuation, but we will examine the basis for the company’s proposal during the statutory consultation period.”

In the letter outlining its proposal to increase member contributions, the company acknowledged the potential difficulty of meeting the additional cost and offered alternative options.

The alternatives to membership of the defined benefit pension scheme were:

(1) opt out of all pension provision and receive a salary supplement of 15%

(2) opt out of the defined benefit scheme and receive a company contribution of 15% of pay into a non-contributory defined contribution scheme.

Walsh added: “The company’s letter is a cynical way to try to persuade members to give up membership of a good defined benefit pension scheme.

“It would be far better if the company explored alternatives that emphasise the benefits of staying in a defined benefit pension scheme, rather than trying to bribe members to opt out.

“Prospect has written to members to explain that nothing is changing right now. We have told them that we will respond to the consultation and that there is no urgent need to make any decisions right now.”