An ex-employee of Swiss banking giant UBS reportedly may leave prison a rich man after he blew the whistle on a huge US tax fraud.

Bradley Birkenfeld turned in thousands of people for trying to evade paying taxes in the United States. But he was sentenced in August 2009 to three years and four months in jail for inciting UBS clients to commit tax fraud.

Bradley Birkenfeld ... jailed for three years. Credit:Reuters

Birkenfeld told CBS on Sunday he felt he had been badly treated after he denounced 19,000 UBS clients who were said to have invested about 20 billion Swiss francs ($A15.05 billion) in secret Swiss accounts.

"I'm the only one going to prison. Out of 19,000 accounts and no Swiss bankers," he said.