The male American lobster is clawing his way toward hegemony. Scientists say his unusually large crusher claw compared with other species can be irresistible to female lobsters and menacing to less-endowed males.

This means war—or at least a trans-Atlantic trade war.

Claw size is at the center of a push by Sweden to ban imports of live Homarus americanus to all European Union countries. The effort began with the release of an 89-page report in December by the Swedish Agency for Marine and Water Management, featuring a full-color, half-page photo of an American lobster and 13 instances of the words “invasive alien species.”

“Once the American lobster is established, it will be impossible to eradicate,” says Gunvor Ericson, state secretary at the Swedish ministry for climate and the environment. The report contends that American lobsters have the potential to spread diseases to Europe’s smaller, native Homarus gammarus.

Sweden says big-clawed Americans could spawn a new generation of hybrids and eventually crowd out European lobsters. The European Commission, the EU’s executive body, is expected to start deliberating the import-ban proposal in June.