The Mandate union has urged the Government to address the rising number of workers trapped in "precarious work" with no certainty about working hours or income.
Mandate represents 45,000 low-paid retail and bar staff.
Addressing the Oireachtas Committee on Jobs, Enterprise and Innovation, Assistant General Secretary Gerry Light said the sector accounted for over 15% of employment in the economy and most are women working part-time.
He said a Behaviour and Attitudes survey of the union's membership showed that 70% had worked in retail for over five years, but less than one-third had full-time contracts.
Mr Light said 40% reported a fall in take home pay since the recession, averaging €109 per week.
Half have had their hours cut, 60% are seeking additional hours and 40% are in personal financial difficulties.
The survey found 70% are less inclined to visit a doctor, while 10% have a second job.
It found 17% claim a social welfare payment and 97% receive no shift allowances.
Half of respondents reported that their hours were changed at least once a month, with only one-third on stable hours.
Mr Light criticised employers for arguing that total flexibility in employment contracts was necessary to be competitive.
He noted that the IMF had said that if "involuntary underemployed" was factored into unemployment statistics, the unemployment rate would rise dramatically.