It is "not uncommon" for Birmingham children's social workers to have between 30 and 40 cases on at a time, according to the council's Unison branch.
"High caseload levels are still extremely prevalent - having between 30 and 40 on at a time is not uncommon," said Chris Cooper, children's services representative for Birmingham's Unison branch.
His comments follow the revelation that the lead social worker on the Khyra Ishaq case had 50 allocated cases when the child died.
This is despite council efforts to improve services since the death of Khyra in 2008.
Cooper said staff shortages were the main problem.
"At the moment there are 100 posts vacant in children's services," he said. "That's 15% of the entire children's workforce and a huge number of those vacancies are in child protection. They just don't have enough social workers."
Birmingham Council has not responded to Community Care's request for information on caseloads.
What are your thoughts? Have your say on CareSpace.
Related articles
Khyra Ishaq social worker had 50 cases on the go
Khyra Ishaq death due to lack of information sharing, says SCR
Ofsted reports only limited progress at Birmingham