The Compact, the agreement that sets out how charities and public bodies should treat each other, says a minimum of three months' notice should be given.
Stoke Council decided to stop its annual £40,000 grant to Communibus in favour of contracting out its community transport services. When the tendering process was delayed, the charity agreed to extend its work for the council until the contract had been awarded.
However, the charity said that when the local authority decided in March to award the contract to a private company, it gave the charity only two weeks' notice its funding was being stopped.
The council denies the claim. A spokesman said Communibus had been told in January that the service was likely to change to another provider and had been kept informed.
Jess Crocker, Compact advocate at the NCVO's Compact Advocacy Programme, criticised the tendering process.
"We respect the right of councils to make difficult financial decisions, but the process in this case has left a small organisation at risk of closure because of the council's unwillingness to follow the Compact," she said.