Credit Suisse Group AG (NYSE:CS) employees are reportedly preparing to sue Swiss regulator FINMA after losing $400 million in bonuses partially tied to the bank's AT1 bonds.

As a part of the takeover in March, the Swiss regulator ordered CHF16 billion of the lender's AT1 debt to be written down to zero, while shareholders received some compensation.

Read: UBS Cites $17B Hit From Rushed Credit Suisse Takeover, Blames Hasty Due Diligence

Lawyers are unsure if claims from Credit Suisse employees could be added to the current claim filed against FINMA or would need to be filed independently, the report added, citing sources with knowledge of the matter.

"We have been contacted by Credit Suisse managers from around the world to see how we could help them," FT said. "There is a lot of overlap between the two positions, but they are not exactly the same."

Credit Suisse had initially asked Finma if the CCAs could be treated differently to AT1s, but employees were told three weeks ago that their awards would be wiped out along with the AT1s. 

UBS said this week that it would book a $400 million gain from the move once it completed the takeover.

Price Action: UBS shares are up 0.10% at $20.11 during the premarket session on the last check Monday.