Twitter has apologised for hosting a frat house-themed party for its staff while the company is in the middle of a class-action lawsuit for gender discrimination.

The party was held on Tuesday by one of Twitter’s San Francisco-based teams for their internal “happy hour”, and involved frat-style accoutrements such as a keg, red Solo cups, and beer pong, all under faux-Greek letters reading “TWΦTTΣR ΓRΛT HΘVSΣ”.

After a female Twitter employee posted a picture of the party on a Facebook group for women in technology, it spread rapidly, with many highlighting it as the latest example of how Silicon Valley culture can, purposefully or not, be exclusionary towards women.

A Twitter spokesman apologised for the party, telling Fusion: “This social event organised by one team was in poor taste at best, and not reflective of the culture we are building here at Twitter. We’ve had discussions internally with the organising team, and they recognise that this theme was ill-chosen.”

The party is particularly embarrassing for Twitter, coming as it does in the middle of its own battle with a class-action lawsuit alleging widespread gender discrimination at the company. Launched in March this year by Tina Huang, a former engineer at the firm, the suit claims that the company’s promotion and hiring procedures fail to ensure adequate diversity in high-level coding positions.

The most recent report into Twitter’s staffing shows it lacks gender diversity. Some 70% of its workforce is male and among its core technology employees that figure rises to 90%. Just eight out 37 (or 21%) of executives and senior leaders are female.