The government considered scrapping 'protected persons' pension rights, granted to workers in the nuclear and electricity industries, as part of the reforms to the state pension.
The protections in the 2004 Energy Act required the companies to provide pension benefits to workers employed at the time of privatisation that are no worse than they would have received in the public sector.
Prospect deputy general secretary Garry Graham said: "This is a significant victory for our members who stood together to make their voices heard. Had the reforms gone ahead they would have allowed employers to unilaterally adjust pension benefits to offset increased National Insurance costs.
"Our members would have been penalised because they made decisions about their financial futures based on promises made to them in the past."
But Graham said he was still concerned about the impact of other proposals in the Pensions Bill to significantly reduce expenditure on state pensions which will result in more losers than winners.
"Although the protected persons regulations remain in force, cost pressures have not disappeared.
"I would like to pay tribute to the many Prospect members who took the time to respond to the consultation and who also lobbied their MPs. I have no doubt that these actions had a significant impact and with such a finely balanced consultation they were almost certainly the difference between the outcome we were looking for and the outcome we feared."