Cambridgeshire County Council is seeking to recover £54.7M from contractor Bam Nuttall and parent firm Royal Bam Group for its delayed Guided Busway project.
The writ was filed on 11 August and relates to damages for break of contract on the design and construction of the scheme.
Zurich Insurance is also named in the action, as the council claims a £7.5M guarantee bond has not been paid.
“Bam Nuttall finally delivered the scheme two years late, but now dispute they should be liable for the overspend,” said a council spokesman.
“The council has a duty to deliver best value for Cambridgeshire taxpayers and we are taking the necessary actions to achieve this.”
The original project cost was £116.2M while the construction fee was £87M. However, the project cost has now reached £151M. Bam Nuttall declined to comment.