The EU is deeply divided over GMO foods. Several EU states have passed laws to control the growing of biotech crops, while others are waiting in the hope that uniform EU rules will be drafted.

Hungary's Seed Alliance, the sector's biggest interest group, said GMO maize might find its way into the EU from the east while decision-makers consider uniform legislation.

The alliance fears that biotech maize is already in use across Hungary's eastern border with EU member candidate Romania, which has no such ban on the GMO seeds.

"We have information that (GMO maize seeds) might have been already imported through cross-border trade, but there is no way to monitor the amount," Janos Turi, Alliance president, told Reuters.

The local anti-GMO campaign chief of environmental group Greenpeace said she also had information about imports of GMO maize from Romania, where biotech soy and maize are already in production.

"This is very unpleasant as we are their neighbours and the GMO crop might also reach other countries through us," Noemi Nemes told Reuters. "A law should be passed, which would set the allowed GMO content of seed at zero percent."

Turi said much lower seed prices in Romania were a big temptation for Hungarian farmers, while in small-scale cross-border trade there is a risk that imported seed purchased is not checked against GMO contamination.

Once the GMO hybrids get into the country, the crop may also contaminate neighbouring maize fields. "We must call to the attention of farmers that they take a huge risk if they do not check the seeds," Turi said.

"This is a tough fight," he added. "(Contamination) is against our marketing interests, as we have a reputation for having a strong non-GMO bioculture, while no market for the GMO is visible in the EU."

Some grains purchasers specify that stocks be certifiable as being free of GMO content. Many consumers in Europe are wary of GMO products, fearing they may have health side effects, while producers of GMO say they are safe.

Turi said Romania adheres to international agreements on seed trade but these do not provide for checking imports for GMO content at the border.

He said the government could clamp down by allowing seed imports to flow through only one border-crossing.