Walsall Council has come under fire after announcing the changes for carers who support elderly and vulnerable people in their homes.
Several providers have said they may have to take on less work in Walsall, while there are also fears they will lose workers who can get a better deal in other parts of the Black Country.
Walsall Council said the policy was included in the current contract with domiciliary care providers in the borough, though it has not previously been implemented.
Previously, carers who were with a patient on a home visit for at least 23 minutes would be paid for the full half hour.
There has been talk of protests, while bosses of some providers have said they have contacted solicitors.
Council leader Mike Bird said the authority needed to make savings but said he was willing to listen to concerns of care bosses.
He said: "Unfortunately whenever you get change people don't like it. I'm aware there is some heat in the system.
"At the end of the day we have only got so much money to go round which means we have got to pay in a different way. I'm sad to say that's how it is.
"People with concerns are welcome to write to us and we will see if we can negotiate with them but sadly there can be abuse of the system and we are looking to make sure we are getting value for money.
"The policy that was laid out to me seems a worthwhile one to introduce."
The change in policy, set to come into force this month, has sent shockwaves through the care system in Walsall, with most providers saying it is a bad idea.
The boss of one care provider told the Express & Star: "This is the worst things I've ever seen. Once they get that pay packet, after they have gone out and done the same shift as normal, there is going to be staff leaving left, right and centre. If you are taking a few quid off carers they are going to be gone."