German tour operator TUI AG has asked Greek hoteliers to sign new contracts spelling out how it will pay its bills in the event Greece leaves the euro zone and starts using a new currency, a spokesman for the company said.

As a responsible company, we should protect ourselves for a potential exit of Greece from the euro zone, spokesman Robin Zimmermann said on Sunday, adding TUI's Nordic unit had sent a letter to the hoteliers.

He was confirming a report in German newspaper Bild, which quoted the letter as saying: If the euro should no longer be the currency (...), TUI is entitled to pay the sum of money in the new currency. The exchange rate shall be made at the exchange rate set by the government.

Tourism is key for Greece's 230-billion-euro (£197.9 billion) economy and accounts for about a fifth of gross domestic product (GDP). More than 2 million Germans travelled to Greece last year, making them the biggest group of visitors there.

The President of the Greek Tourist Board, Andreas Andreadis, told Bild that several Greek hoteliers had received the letter from TUI, the owner of London-listed TUI Travel , and were asked to sign it.

No hotelier will do that and we turned to the Greek Ministry of Tourism. TUI can not put pressure on hoteliers to sign such a thing, he was quoted as saying.

(Reporting by Harro ten Wolde; editing by Gunna Dickson)