EU environment ministers meeting in Brussels today (9 March) will vote on a Danish compromise designed to break a deadlock that has split governments since the draft rules were proposed in 2010.
The rule change was drafted by the executive European Commission to try to unblock EU decision-making on GM crop approvals, which has seen just two varieties authorised for cultivation in more than 12 years.
But strong opposition from several EU countries has stymied efforts to agree the new rules.
"Things are still looking extremely difficult," Danish Environment Minister Ida Auken, who will lead the discussions, told Reuters.
"We have a small blocking minority at the moment, but we still hope that we will dissolve it, and it's going to come down to one or two countries in the end."
While France, Germany and Belgium are unlikely to reverse their opposition, Britain and Spain had initially appeared willing to support the Danish compromise, EU sources involved in the talks said.
But London and Madrid are now expected to vote against the plan unless certain concessions can be made. Auken would not speculate on what possible changes could win their support.
"I'm going to try to use the argument that, why not give the 22 countries the right to say 'no' when they really want this right?" Auken said. "Why stop somebody else from having that right to say 'no' in their own land?"
The Danish plan would first see companies seeking EU approval to cultivate a GM crop try to agree in advance not to market the product in countries that do not want to grow it, in return for approval to grow the crops in other EU states.
If that proved unsuccessful, countries would then be able to cite certain environmental or other concerns to ban cultivation in all or part of their territories, provided they respect World Trade Organization and EU internal-market rules, the draft compromise showed.
Auken said if no agreement could be reached on Friday, Denmark would consider holding further talks on the plans only if some of the opposing countries showed a willingness to reach a deal.
Environmental campaigners have dismissed the Danish compromise, saying it fails to offer governments sufficient legal grounds to ban GM crops when compared with those proposed by lawmakers in the European Parliament.