The UK Homecare Association (UKHCA) has labelled the move to per minute billing as "completely inappropriate".
The intervention comes after a council memo leaked to the Express & Star revealed elderly and vulnerable people were being put at "risk" by a backlog of cases that hadn't been picked up.
Some providers say they have taken on less work in the borough as a result of the pay change as they fear losing carers to competitors working elsewhere in the Black Country where pay is higher.
Walsall Council has refused to back down over the move despite increasing anger in the care sector. It has also triggered a one-year extension clause in its contract with providers amid threats from some they were willing to walk away.
Previously, carers who were with a patient on a home visit for at least 23 minutes would be paid for the full half hour.
UKHCA spokesman Colin Angel said: "The impact of councils paying for social care by the minute: there’s a backlog of demand for home care by people relying on support from Walsall Council.
"The situation with Walsall Council doesn’t sound like their home care contract is working well, if their providers are accepting fewer care packages.
"Councils paying for home care by the minute, particularly at a low hourly rate, has a direct impact on the terms and conditions employers can offer the workforce. Does anyone think that’s a good way to work?"
The organisation's chief executive Jane Townson also weighed in and revealed Walsall Council was one of only three local authorities in the country to fail to respond to a Freedom of Information request on their care pay rates.
She said on Twitter: "Walsall was one of only three councils that failed to respond to repeated UKHCA FOI requests for data on home care fee rates in 2018 - wonder why.
"Now Walsall has imposed per minute billing and they wonder why there’s unmet need. We’re going to submit another FOI to Walsall re fee rates."
Walsall was 1 of only 3 councils that failed to respond to repeated @ukhca FOI requests for data on #homecare fee rates in 2018 - wonder why. Now Walsall has imposed per minute billing & they wonder why there’s unmet need. We’re going to submit another FOI to Walsall re fee rates https://t.co/kSRQdWgE2Z pic.twitter.com/gxvNmiWTTv— Jane Townson (@drjanetownson) October 11, 2019