Near-full employment is masking the issue of "precarious employment" which is affecting hundreds of thousands of households nationwide, according to SIPTU.
While more people than ever before are at work and official figures show that unemployment is as low as during Celtic Tiger times, the union says that many people working do not have security about their future.
SIPTU held a conference in Waterford city today on precarious employment and said that in the Waterford area 4,100 out of 39,000 employees are temporary while 5,100 workers are part-time because they cannot find a full-time job, or are caring for a family member.
Nearly one in three workers in Waterford, 12,800, cannot afford to meet an unexpected expense and SIPTU says that a similar proportion is likely to be in effect across the country.
"The growth of such in-work poverty can be directly linked, in many cases, to the spread of precarious work practices," SIPTU Waterford secretary David Lane says.
"These include the use of rolling short-term contracts, non-voluntary part-time employment, enforced self-employment and other employment relationships which result in workers being low paid and insecure concerning their finances."
Nationally, according to the union, 68% of temporary contracts last less than a year - up from 40% before the recession took hold in 2008.
Meanwhile, temporary agency workers make up 2.7% of all employees in Ireland at the moment, up from less than 1% pre-crash.
In Co Waterford, 6,900 workers are at risk of low pay and nationally 22% of all full-time employees fall into this category, which means they earn less than two-thirds of the median wage.
SIPTU wants civic and community groups to "fight for a better working lives throughout the city and county," according to deputy general secretary Ethel Buckley, and is also encouraging workers to join a trade union to give them more power on a collective basis to improve conditions.