New York-based hedge fund firm Fir Tree Partners has upped the pressure on embattled Swedish landlord SBB by raising 'serious concerns' about the conduct of the company's directors, according to a report by Bloomberg.

The move comes as SBB's second largest shareholder quit the border.

The report cites a private letter sent to SBB by Fir Tree and seen by Bloomberg as claiming that the firm may be held criminally and civilly liable if it doesn't act in accordance with its duties.

Fir Tree reportedly holds about €46 million ($49.6 million) of the landlord’s notes — representing around 1% of its total bond stock, SBB said — and last month demanded its money back based on an alleged breach of debt terms.

SBB responded by saying it regards the claim as groundless.