The proposed badger cull in north Pembrokeshire is facing a new legal challenge.
The Badger Trust has been told it can appeal against the outcome of a judicial review that backed the Welsh Assembly Government's plans.
The cull aims to cut the rate of tuberculosis in cattle, but opponents say it is not justified by science.
The assembly government says the cull will go ahead, but the trust says it should be suspended pending the appeal.
The Badger Trust asked for the right to appeal against the outcome of a judicial review held in April, which upheld the government's right to mount the cull.
It argued that the assembly government and Rural Affairs Minister Elin Jones had not shown that a cull would "eliminate or substantially reduce" the rate of TB infection, as the law meant it had to, and that ministers had a duty to weigh the harm to the badger population against the possible benefits to farmers, but had not done so.
Mr Justice Elias agreed that these two points were "arguable", and granted the trust leave to appeal.
"Overall, it casts a shadow over the impending cull start in Wales," said Gwendolen Morgan, the trust's legal adviser.
"This should give the minister pause for thought before proceeding, as to start a cull and then stop summarily would be likely to cause a serious spike in TB," she told BBC News.
The largest study of culling anywhere in the world - the UK-based Krebs Trial - showed that unless it is done comprehensively, culling makes the problem worse, because it disturbs badgers' social groups, inducing them to roam further afield and infect more cows.
However, a spokesman for the assembly government said the cull would proceed.
"It is our intention to begin to remove badgers from the intensive action pilot area in west Wales as soon as preparations are complete," he said.
"This disease has cost the taxpayer £100m over the last 10 years in compensation payments alone.
"If we are to be successful in eradicating the disease from Wales, we must tackle all sources of infection, including the reservoir of infection in wildlife."
In addition to the cull, farmers in the pilot area will see more frequent testing of their cattle, as well as restrictions on movements of their herds.
The exact date on which the cull is due to begin, and the location of the first kills, are closely-guarded secrets, with the government fearing disruption by campaigners.
At least 1,500 badgers are due to be killed during the five-year programme.
The UK government is likely to approve "targeted" badger culls in England in the next few years.