A US diplomat did not deny the existence of the note and said Washington regularly shared views with Cyprus on issues of concern.

Under EU legislation, each state is free to display biotech food as it wishes.

The bloc has tough rules for the labelling of food that contains genetically modified organisms, or GMOs. If conventional food contains more than 0.9 percent of authorised GMOs, it must be labelled as such throughout the 25-nation bloc.

"We want to put better information at consumers' disposal on what they are buying," said George Perdikis, a member of the Greens' Party which tabled the proposal in parliament.

A note which Perdikis said was released by the American Embassy in Nicosia, and which was seen by Reuters, urged parliamentarians to oppose passage of the bill.

"The bill is in essence a poke in the eye of the US, which is the leading developer and producer of agricultural biotech products," the note read.

"The bill is tantamount to a non-tariff barrier to trade in biotech goods and as such is in violation of your obligations as a member of the WTO. It may also be inconsistent with your obligations as an EU member," the note states.

Perdikis, a junior partner in Cyprus's centre-left government coalition, said he came across the note in his parliamentary documents.

"This is blackmail. It speaks of harming bilateral relations. It is very serious," he said.

A US embassy spokesperson said: "The United States shares the goal of the parliament and the government of the Republic of Cyprus to protect the health and well-being of all Cypriots but it is of course up to the parliament to decide what laws to pass.

"We do however regularly share our views with Cypriot officials on issues of concern."

European public opinion is consistently hostile to genetically modified products, fearing negative health and environmental effects. Advocates of biotechnology say it is safe and will help eradicate world hunger by improving food supply.