Up to 40 construction firms were found to be ripping off staff over pension entitlements last year, according to the Pensions Ombudsman.
Launching his second Annual Report, Paul Kenny said it was depressing that some employers were deducting money from pay packets but not passing it on to their employees' pension schemes.
The number of complaints to Mr Kenny's office jumped by one-third to 389 in 2005, compared to 297 files in 2004.
In 2005 a total of 76 formal determinations were made, of which 24 were upheld, compared to 23 determinations in 2004 of which only 7 were upheld.
However, he added that it was important to note that in addition to the formal determinations a further 146 cases were settled by mediation, 95 of which ended in some concession to the complainant.
In addition, 43 cases were disposed of with general advice while 93 were outside his terms of reference, either because they were out of time or referred to something outside his terms of reference.
But 50 complaints related to 40 construction firms.
"There are still depressing numbers of complaints about the failure of employers to register members or pay contributions," he told a press conference.
"Worst of all is the theft by employers of contributions that have been deducted and not remitted to the pension scheme."
Mr Kenny also said he was concerned about the low level of pension cover for women and he urged young people to take out pensions when they started their first job.
Welcoming the report, the Minister for Social and Family Affairs Seamus Brennan said the Government would be publishing a Green Paper discussion document on pensions in coming months.
"We cannot have a situation in the long term where people don't have a retirement package when they stop working," he said.