Karmenu Vella has unusual credentials for a man selected to be the next European commissioner for the environment. The 64-year-old politician is a long-serving member of Malta's Labour government, which is accused of direct involvement in the widespread slaughter of birdlife on the island – including many endangered species.

Every spring and autumn, thousands of migratory birds – including quails, song thrushes and brood eagles – pass over Malta as they fly between northern Europe and Africa, only to be greeted by thousands of local hunters who gather in trucks bearing slogans like "If it flies it dies". They duly open fire on the birds.

"Turtle doves have suffered a catastrophic decline in western Europe, including Britain. Yet the Maltese government continues to allow them to be shot in their thousands every year," said Andre Farrar of the RSPB. "This slaughter has widespread implications and involves dozens of rare species, many of them regular visitors to the British Isles."

Campaigners say Malta's bird culls, which have intensified over the last two years, have been specifically encouraged by its Labour government. For example, new rules have extended shooting curfews, which previously limited the hours when hunters are permitted to fire at birds each day. Such moves have helped make Malta the ecological pariah of Europe.

The prospect of Vella – a leading member of the Labour party – being put in charge of the European commission's environment portfolio, which has specific responsibility for birdlife and its habitats, has horrified green groups, campaigners and wildlife protection organisations.

Vella's candidacy has also alarmed MEPs, who will subject him to intense cross-examination over his involvement in the bird culls on Monday. Many also fear that the newly elected commission president, Jean-Claude Juncker, is planning to weaken the powers of Europe's environment directorate and that Vella has been selected specifically to implement these changes.

"To give the nature brief to a politician from Malta, where such wildlife abuses occur, has a very suspicious smell, particularly against a background in which Europe seems to be contemplating a weakening of its environmental controls, despite their great success in the past," said Farrar.

This point is backed by Steve Micklewright, head of Birdlife Malta. "Twenty years ago, there were quite a number of places in Europe where the slaughters of migratory birdlife took place," he told the Observer. "They were held in parts of France, Spain and Italy. Thanks to Europe's bird directive, that situation has improved greatly. We still have the slaughter in Malta and there are also problems in Cyprus, but things are undoubtedly better. However, by putting Vella in charge of an environment directorate that is threatened with reduced powers, a very worrying message is being sent to the rest of Europe."

The Maltese government has said it will hold a referendum on whether it should continue to allow the annual bird shoots. The current autumn cull has been suspended following outbreaks of violence between bird watchers and hunters. "It would have looked very bad if these battles were going on while Vella was being grilled by MEPs," said Micklewright. "So there has been a temporary suspension. It won't last long."