UBS is sitting on losses that could be as high as $350 million stemming from its investment in the Facebook initial public offering, and is preparing legal action against Nasdaq as a result, people familiar with the matter told CNBC.

That loss is some ten-times more than the $30 million number that is currently being speculated in the market by others.

The issue has to do with the failure to get confirmations and executions from the Facebook trade.

These people said UBS wanted 1 million shares, but when it did not receive confirmations, it repeated the order multiple times and was left with much more than it intended.

"Given the size of our U.S. equity business and our role as a major market maker, UBS was affected by these issues, as we believe other market participants may have been," UBS said in a written statement.

"Consistent with our policy on market comments on our positions or intra-quarter performance, we are not disclosing the amount of the loss, which is not material to UBS," it continued. "We are continuing to consider avenues to recover our losses in this matter, but have not yet taken legal action."

There have been reports in the market that UBS's market-making arm is down $30 million to $35 million, but UBS itself has not disclosed the full extent of its losses related to Facebook.

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