Figures from the Central Statistics Office show that the number of workers who had a pension in the fourth quarter of last year fell to 46.7% compared to 51.2% in the fourth quarter of 2009.
The figures are contained in a special study - the first since 2009 - on pensions in the CSO's latest quarterly Household National Survey.
Today's figures show that 42% of workers said they expected an occupational or personal pension would be their main source of income when they retired.
But the proportion of workers who expected the state pension to be their main source of income rose from 26% in 2009 to 36% in the fourth quarter of last year - highlighting the deepening pension crisis facing the country.
Today's figures show that more men than women had pension cover - with the level of coverage for male workers coming in at 47.2% and for female workers at 46.2%.
They also reveal that pension coverage was lowest amongst the youngest workers. Just 14.1% of workers aged between 20 and 24 had a pension in the fourth quarter of last year, while 36% of workers aged between 25 and 34 had a pension.
The CSO said that pension coverage was highest among workers aged between 35 and 44 years of age, standing at 55.3%.
Three out of every ten self-employed people had pension coverage in the three month period under review, down from a level of 36% in the same time in 2009.
The most common reason given by people for not having a pension was an issue of affordability. 39% of workers said they could not afford to pay into a pension, while 22% of workers said they just never got around to organising one.
Meanwhile, 68% of workers said they intended to retire between the ages of 60 and 69 years of age, while 8% said they had no intention of ever retiring.
54% of the workers in the CSO study said they had a defined contribution pension, while 46% had a defined benefit pension.
Danny Mansergh, Principal with consulting firm Mercer, said the CSO study "highlights that Ireland's pension crisis is getting worse not better.
"More workers expect the State pension to be their main source of income in retirement. However, the changing population structure is likely to render the current level of our state pension unsustainable in the future.
"A system of auto-enrolment for all or most workers into pension plans provides a potential path to sustainable retirement for future generations. Doing this will improve participation rates and ultimately help to reduce the risk of future pensioners facing poverty," he added.