Danny Molloy, Midlothian Council's deputy leader, and Malcolm McEwan, the social work director, resigned last week after an HMIE report found that children at risk of abuse might not be getting the help they needed.
Unison, which represents many of the staff whose work was scrutinised in the report, said that recruitment and retention had been problems in the department for some time. It explained that social work team leaders raised a grievance action in April 2005, alerting management to the seriousness of the situation, and that in July last year other social workers outlined concerns about staffing, organisation, IT support and administration.
Action was not pursued, Unison said, because staff were promised solutions, but it is worried that the service is still being run with many inexperienced social workers and agency staff, while experienced staff are leaving.
Lesley Greig, branch secretary of Unison's Midlothian branch, said: "We have been working with the council to try and put reforms in place to counter these problems, but it is clear that we still have a way to go."
Hugh Henry, the minister with responsibility for social work, demanded immediate action, and Adam Montgomery, the Midlothian Council leader, pledged that all improvements recommended in the report would be made as quickly as possible.
The relevant agencies - as well as the local authority, the health services, the police, the children's reporter and others - have four months to submit a joint report outlining progress made and future plans.
A follow-up inspection is due within one year.