Financial services news group Bloomberg was facing questions on Friday about how reporters used information about clients gleaned from its widely-used terminals.

The New York Post reported that journalists at Bloomberg had been caught using the financial news service’s $20,000-a-year terminals to “spy” on Goldman Sachs bankers.

The Guardian also understands that JP Morgan also has concerns about how Bloomberg used information from its terminals while pursuing stories about Bruno Iksil, the trader known as the London Whale, who was blamed for massive losses at the bank last year.

Bloomberg said it had blocked journalists’ access to client data within 24 hours of receiving a complaint from Goldman.

The concerns raised by Goldman could be a major headache for Bloomberg, which makes most of its money from renting the terminals to traders. It now faces complaints from other Wall Street banks that believe they too were spied upon by reporters in a breach of confidentiality.

The Post said that a Bloomberg reporter asked a Goldman executive if a partner was still with the firm, saying that he had not logged into his terminal for some time.

More than 300,000 of the world’s most influential people in finance including top bankers, treasury officials and hedge fund managers have access to a Bloomberg terminal. Almost all users are identified by name and their terminals are often highly tailored to give them access to the financial information they need. Access to the types of information those users are looking up would give a reporter invaluable insight.

“Limited customer relationship data has long been available to our journalists, and has never included clients’ security-level data, position data, trading data or messages,” Bloomberg said in a statement. Bloomberg has now blocked journalists from accessing that data.

Bankers said they believed the reporters had access not only to log-in information but also to whether the users had called the help desk and what information they had wanted help with. “I don’t think anyone realised how much information the news desk had access to,” said one Wall Street executive.

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