Add Citigroup to the list of banks crying foul at the way Nasdaq handled automated trading in the May 18 Facebook IPO.

The New York-based financial services giant said the technical snafus that marred the launch of trading in the social networking firm's shares amount to 'gross negligence' on the part of the Nasdaq Stock Market.

In a letter to the Securities and Exchange Commission, Citigroup says the mess caused its market-making arm, Automated Trading Desk, to lose around $20 million, according to Reuters.

Citigroup is asking the SEC to make Nasdaq fully liable for all IPO-related losses.

Nasdaq has set aside $62 million, but UBS says it's owed more than $350 million and Knight Capital says it's owed $35 million.

Here's the Reuters report.