MILFORD, CONN. – The Subway sandwich chain is ending its decades old free sandwich promotion, company officials said yesterday, amid concerns that counterfeiters were creating and selling copies of the restaurant’s proof-of-purchase stamps and cards.

Subway, the nation’s second largest restaurant chain, joins a growing chorus of businesses – from pharmaceutical companies and cigarette manufacturers to recording studios and clothing designers – that have seen fraud hurt their bottom line.

Under the Sub Club promotion, which had run in some form since the 1980s, customers received a stamp for every 6-inch sandwich they bought. A full card of eight stamps could be redeemed for a free sandwich.

But thousands of stamps are for sale at online auction sites and company officials said franchise owners were increasingly discovering counterfeit stamps.

“It’s possible some of the stamps got by and we didn’t even know,” said company spokesman Kevin Kane. “It’s possible we don’t even know the extent of it.”

Each restaurant can set its own timeframe, but the promotion will be phased out companywide by October 1, Mr. Kane said. He said the company had been considering whether the promotion was outdated for some time.

When the company discovered rolls of stamps available online, Mr. Kane said, it sealed the promotion’s fate.

“All that effort and you’re getting free subs,” Mr. Kane said. “It wasn’t a cruise. It wasn’t a trip to the Bahamas. You’re getting free subs.”