A Long Island Internet entrepreneur is facing up to 20 years in federal prison for running up $5 million in credit card charges, authorities said today.

Daniel Greenberg, 38, allegedly made more than 70,000 unauthorized charges – totaling more than $5 million — after the victims made Internet purchases at West Hempstead-based Classic Closeouts.

When the shoppers complained to their banks and credit card companies about the charges, Greenberg allegedly told the card issuers that the customers had enrolled in a “frequent shopper club.”

As a result of that assertion many banks and credit card companies refused to issue credits, leaving the victims stuck with the fraudulent charges, authorities said.

Greenberg appeared briefly in Brooklyn Federal Court Friday, but his bail hearing was postponed until next week.

Leo Kimmel, Greenberg’s lawyer, said, “He denies having done any criminal act.”