Aland, an archipelago in the Baltic Sea, is to become an unlikely battleground in European ferry operators' campaign to preserve lucrative sales of duty-free goods on trips within the European Union. Two of Europe's largest ferry operators - Silja Lines and Viking Line of Finland - are planning to exploit the tax-free status of the 6,500-island archipelago by rerouting their Baltic Sea ferries via Aland.

EU ministers agreed in 1992 to abolish duty-free sales within the 15-country single market from mid-1999. But a powerful lobby of airports, airlines, ports and ferry operators is campaigning to reverse the decision.

The Aland archipelago, although technically Finnish territory, was granted special tax status within the EU when Finland joined in 1995. By calling at Marieham, the capital of Aland, Silja and Viking could preserve tax-free sales on services within the EU.

Industry analysts said the plan could prompt other ferry operators to examine similar loopholes, such as stopovers in the Channel Islands on the so-called "long sea" routes between Britain and France.

The Aland move by Silja and Viking - which together carry two and a half million passengers a year between Stockholm and Helsinki - marks the latest stage of a determined campaign by ferry operators to preserve the duty-free trade.

Finnish ferry operators enjoyed total revenues of 4.7 billion Finnish markkas (£914 million) from duty-free sales in 1995, the latest figure available.

Stena Line of Sweden, the world's largest ferry company, claims up to 80,000 jobs could be lost in Europe with the abolition of tax-free retailing and said it would watch the Finnish proposals closely.

Silja, meanwhile, warned it would consider re-routing its Helsinki-Stockholm service via Tallinn, the Estonian capital, if the European Commission tried to block the Aland plan.