David Bowles, the RSPCA's head of public affairs, said the cull - an attempt by the Government to eradicate bovine tuberculosis - was not necessary.
The Department for Environment, Food and Rural Affairs (Defra) refused to confirm or deny reports from the BBC that the cull would be extended.
"The RSPCA believes there are better ways to tackle bovine TB," Mr Bowles told BBC Breakfast.
"It's more expensive to cull. It's more inhumane to cull. It doesn't sort out the problem even if you do it properly."
The BBC reported that Tony Francis, a farmer who had TB in his herd near Okehampton in Devon, said he had signed up to one of the new cull zones to try to prevent the disease from returning.
A Defra spokeswoman said: "Natural England is currently considering applications for further badger control licences as part of the usual licensing process.
"England has the highest incidence of TB in Europe and that is why we are taking strong action to deliver our 25-year strategy to eradicate the disease and protect the future of our dairy and beef industries.
"Badger control in areas where TB is rife is one part of our long-term plan, which also includes strengthening cattle testing and movement controls and improving biosecurity on farm and when trading."
