Dozens of council-employed care workers may have been paid below the minimum wage, a leaked report has warned.
Days after meeting bosses at Cheshire East Council to discuss the concerns, the report's author lost her job.
A Conservative councillor has demanded an investigation into both the contents of the report and the way in which Sue Wallace has been treated.
The council said it was "inappropriate" to discuss staff matters but denied breaching minimum wage regulations.
The report, written by the senior HR officer in October and seen by the BBC, warned the average monthly pay of some social care staff was likely to have fallen below the minimum wage.
The claim centres on the number of "sleep-in" shifts - paid at a lower rate than other duties - allocated to some staff.
While on night shifts, employees providing care in people's own homes are allowed to sleep, providing they can be woken to deal with any incidents.
According to minimum wage legislation, employers must take into account shifts where staff are allowed to sleep as long as they are "at work and under certain work-related responsibilities".
Such "sleep-in" shifts were paid £34 for eight to ten hours' work.
Ms Wallace's report said the monthly pay of some employees would only have reached the hourly national minimum wage - then £7.20 for over 25s - if they worked a number of additional hours per month at their regular rate.
Some staff, the report said, worked 11 "sleep-in" shifts in a month which prevented them from working enough regular hours to lift their total average hourly rate to the legal minimum.
The report says Cheshire East Council "looked at" the issue "a couple of years ago", but "the decision then was 'to do nothing'."
Tim Ellis from public sector union Unison's North West of England office, said the pay of staff working the shifts at many care providers was "a disgrace".
"They're not even paid the legal minimum for all the time they are required to be at work, and are at work," he said.
"It is a problem, and we have raised it with a number of councils."
Cheshire East Council said it commissioned an independent review after Ms Wallace's report was submitted.
It added it "takes both the welfare of staff and its legal obligations very seriously" but would not comment further "until the review is complete".
'Fear of retaliation'
The BBC understands Ms Wallace lost her job in December - five days after she met a manager who had been nominated to investigate her concerns.
Ms Wallace submitted her report under the council's whistle-blowing protocol a month after she had sent it to senior colleagues.
Conservative councillor David Marren has called for the Conservative-controlled authority to investigate.
"Whistle-blowing is usually a last resort for employees because those that speak out against wrongdoing fear retaliation," he said.
"This claim needs to be quickly and properly investigated and if the claim is correct appropriate action taken to reinstate the individual."
The council said it would be "inappropriate" to comment on "issues pertaining to individual staffing matters".
Cheshire East councillors voted to pay all staff the living wage, set at the higher hourly rate of £7.85, in February 2015.