Nipsa said the strike action came after a period of negotiations with the Department of Health, which failed to address the problem of staff shortages.
Damien Maguire, who has been a social worker for 20 years, said some staff were working 50-60 hours every week.
“We can’t do this anymore,” he said.
“We can’t have our members crying, leaving the profession, stressed out, retiring early, leaving to go to other jobs that they don’t necessarily want to go into.
“This is people’s lives, it’s children’s lives and it’s families’ lives but it’s also the lives of those social workers who have lived experience of what it’s like to work in the system.”
The strike action is due to last until 10 May.
The has contacted the Department of Health for a response.