Any change to the terms and conditions of a contract, whether it be in relation to hours worked, pay, pensions or anythign else, should be done in consultation between the employer and the employees (or their legal/expert representatives). If the opportunity to contribute to the dialogue and to negotiate a more equitable solution hasn't been offered then a strike seems to me to be the only way forward.
Having said that I think it needs to be recognised by Public Sector workers, as much as it is by Private Sector workers, that this is 2013 and the employment market, the financial state of the planet, and society as a whole have changed significantly over the last half century or so. A contract signed in 1981 will have been based on how the employment market, and how the world in general, worked in 1981. 32 years later virtually everything has changed, it's unrealistic to expect that decisions made over 3 decades ago would still be appropriate now.
Take pensions as an example. In 1981 men were expected to live, on average, until they were 70.8 years old, women until they were 76.8. Pensionable retirement age (for company pensions, not state ones) was 65 (lets assume it was 65 for all, as opposed to 60 for women, which it may have been in some cases).
Now, lets assume these people had a pension of £15,000 a year.
That means 15,000 x 6 years for men = £90,000 per man for his pension.
That means 15,000 x 12 years for women = £180,000 per woman for her pension.
Now, in 2011, men were expected to live, on average, until they were 78, women until they were 82.1. Using the same figures (£15,000 pension, 65 retirement age) you get the following.
£15,000 x 13 years for men = £195,000 per man for his pension
£15,000 x 17 years for women = £255,000 per women for her pension.
So, without any changes to the pensions at all, there now needs to be an additional £105,000 per man and £75,000 per woman found to fund their pensions, for no other reason than people are living for longer. Where does the extra money come from? If the terms and conditions of those employees can't be changed then it can't come from the employee, so therefore it comes from the taxpayer. Why? Why, when the pensions of a large number of taxpayers are being decreased, should they be asked to foot the bill so public sector workers pensions can remain at their very high standard? The solution seems simple, either change the terms and conditions of public sector employees so they have to contribute more (thus keeping the pension they have now) or else decrease the pension they will get (by changing from Final Salary to Average Salary, or Money Purchase, by increasing the retirement age etc).