An analyst at Swiss bank UBS has sent an accidental email that caused the bank to be dropped by a major client, General Motors.
The email disclosed pricing and other details of GM's planned $13 billion share issue, according to the Financial Times. It was reportedly sent to more than 100 people.
UBS is understood to have lost $10 million (£6.2 million) in fees as a result. It declined to comment.
In a filing with the US Securities & Exchange Commission, General Motors said UBS could not remain an underwriter on the deal because if it did, investors buying stock could seek refunds or damages.
It is not known what disciplinary action UBS has taken.
The news highlights the ease with which sensitive data can mistakenly be sent to the wrong email lists or addresses. In 2008, oil giant BP reportedly sent an email to staff warning them not to communicate electronically on its then much-delayed Thunder Horse platform.
More recently, emails sent by BP around its disastrous Deepwater Horizon drill have emerged in high profile US investigations into the oil spill. In one instance, a BP engineer, writing about a cementing decision that was criticised as "rushed" by the commission, wrote: "Who cares, it's done, end of story, we'll probably be fine". That email was presented as evidence into the inquiry.