The number of part-time employees who are not being given enough working hours has risen by 12,000 since 2012.
A survey by the trade union Mandate claims there are now 147,000 "under employed" people working in precarious part-time, freelance or low paid jobs.
That compares to 135,000 people two years ago.
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Gerry Light is Assistant General Secretary of Mandate, which holds its biennial conference in Killarney today.
He says the union is putting pressure on retailers to give contractual entitlements to their part-time staff:
