SIPTU is warning thousands of people will be left facing a financial "cliff edge" if the government increases the pension age.
Under the proposal, the pension age will increase from 66 to 67 in 2021 and then to 68 in 2028.
The union is today launching its new STOP 67 campaign calling for the decision to be reversed.
Frank Connelly from SIPTU says the whole thing has been badly thought out and will hurt people if it goes ahead.
"They're reaching 65, they've realised that they are not entitled to get their pension for another two years if this law goes through," said Mr Connelly.
"It is an obscenity that people are forced to go onto jobseeker's benefit, go down to the local social welfare office and be told that they are expected to look for a job or told that they are only eligible for jobseekers after working for 30 or 40 years."