Lotus Home Care Wakefield offers personal help to more than 150 local people within their own homes.
The Care Quality Commission (CQC) has judged the service is failing after whistleblowers told them carers were frequently arriving late to appointments.
The CQC's report found one carer was working shifts of around 15 hours across three consecutive days.
But Lotus, whose local headquarters are on Denby Dale Road, believe the verdict is unfair and say the problems have been caused by Covid-enforced absence among its staff.
The firm's regional manager said he was confident the service would be rated 'good' again, following the end of the pandemic.
In their findings published this month following snap inspections in March and May, the CQC said that people "did not always receive consistency" in the care they received.
The watchdog added: "One relative told us their relative had 27 different care staff within a 13-day period."
Carers told inspectors that the rota was "ridiculous" and "unmanageable" with one adding, "11pm would be your last call and then you'd start back at 6.30am the next morning.
"I have raised this and said I need a break, but nothing gets done."
The report said: "We saw one staff member's rota started before 7am with client calls booked into until 10.30pm with the next two consecutive days being similar.
"This meant staff were working very long days with consecutive early starting times and late finishes.
"We raised our concerns with the registered manager who told us they signed off the weekly rotas and care staff had the choice if they wished to work all four shifts before accepting the shift."
The report said however that clients and their families were positive about the care they received.
One said: "There are some lovely (staff); they bend over backwards, they're outstanding."
But feedback was more critical of the service managers, with one client saying, "The care staff I cannot fault, it's the times that are a problem."
In response to inspectors' findings, Lotus said they were "very disappointed" with the inadequate rating, adding that its branches in York, Huddersfield and Rotherham had recently received positive grades.
Regional manager Gerry Petts said: "We use state of the art care rota software to ensure all care is delivered on time and in a consistent manner.
"This last year has been incredibly challenging for the sector, with high sickness and isolation levels causing a strain on the service which has resulted in inconsistent call times.
"With the pandemic restrictions loosening up, and as a result of our intensive recruitment drive, we are already seeing quality care staff return to jobs resulting in consistent care being delivered."
Mr Petts said Lotus was "investing significantly", hiring an additional manager for its Wakefield branch and purchasing new technology to make the service less reliant on paper documents.
He added: "We are confident that our Wakefield rating will return to the usual good rating we enjoyed prior to the pandemic."
Local Democracy Reporting Service