Nearly two-thirds of retail workers are earning under €451 per week.
The Mandate trade union is calling for a Cost of Living wage to be introduced.
The union, which represents retail workers, says the National Minimum Wage is no longer fit for purpose and should be replaced.
The claim's been made by the Mandate trade union ahead of the publication of its 'Smoke and Mirrors' report.
A survey of 3,000 members by the union last July, found 21% were earning more than the weekly Living Wage of €502, while 64% were earning below €451 per week.
Mandate says the low earnings are mainly due to the relatively low number of working hours available to retail workers, with the CSO showing retail staff work 72% of the average national working week.
The union is also calling for a change in the law to allow workers to do more than their contract entitles them to, so they can increase their hours and earnings when possible.
Dr Conor McCabe, a researcher with the Queen’s University Management School, Belfast – who prepared the report for the union – said many workers in the sector want to work more hours.
“The Mandate survey shows that 75% of the respondents were on a banded-hours contract and, of this cohort, over 50% were on a contract of 31 hours or more a week. A significant number of these workers, 40%, would like to work more than their banded hours".
