Two women who lost their jobs at Twitter after Elon Musk took over are suing the company, claiming recent lay-offs disproportionately affected female employees.
About half the social media network's workforce were let go early last month after Mr Musk bought the company for $44bn.
He subsequently told those remaining that they would need to work at "high intensity".
"Going forward, to build a breakthrough Twitter 2.0 and succeed in an increasingly competitive world, we will need to be extremely hardcore," he said in a message.
"This will mean long hours at high intensity. Only exceptional performance will constitute a passing grade."
Speaking outside a federal court in San Francisco, Ms Liss-Riordan said she wanted to show that the "richest man in the world is not above the law".
She added: "We are arguing that the arbitration agreements (signed by Twitter staff) are not enforceable.
"But if we have to go through arbitration one by one, we are ready to do that."
Twitter has not yet responded to a Sky News request for comment.
Earlier this week, it was reported that bedrooms had been installed in Twitter's San Francisco offices.