Depending on the country, if the pension comes from social security/government, the way is a Pensioners'Union to protest, collecting signatures, doing the necessary job in order the government to release pensions. More or less what the 3 users above have mentioned. In any way, if social security got totally broken, maybe there is not too much to do.
If the pension is private, for ex. coming from a private contract with a credit society, whose customers paid periodical fees and the credit society refuses to pay the pension when the contract is 100% fulfilled, there could be enough reasons to sue the company.