The Welsh Assembly Government has retracted a claim made in an official leaflet sent to 26,000 homes in a proposed badger cull area.
The leaflet said previous trials had shown such culls could reduce TB in cattle by as much as 50% in six months.
It should have said culls could start to show a benefit after six months
The government blamed an "editing" error which it quickly tried to correct but campaigners have called into question the consultation's validity.
The leaflet was designed to raise awareness of the assembly government's consultation into its new plans to tackle bovine TB.
An annual badger cull is planned over five years for north Pembrokeshire and part of Ceredigion.
Opponents had wanted a vaccination programme instead and a legal challenge had halted an earlier plan.
Campaigners against the cull said the fact that the leaflet error was so widely circulated called into question the whole validity of the consultation.
Celia Thomas, of Pembrokeshire Against The Cull, said: "It was our suggestion as a campaign group that they contact all the households in the pilot area to make sure they knew the consultation was taking place, and then they produce something with a completely misleading statement in it about the effectiveness of a cull.
"It could lead people to think that a cull could be much more effective than it actually would be, and calls into question the validity of the whole consultation process."
The leaflet claimed that: "Previous trials have shown that culling badgers can reduce TB in cattle, by as much as 50% in six months."
However, this was later said to be an "editing" error, and should have read: "Previous trials have shown that culling badgers can reduce TB in cattle. Culling can start to show a benefit in six months."
An assembly government spokesperson said: "As soon as we spotted the error in late October we took action to correct the problem.
"This included sending a letter from the chief veterinary officer for Wales to local papers in early November, sending a correction to all addresses that had received the leaflet originally and withdrawing the leaflet containing the error from display."