The two groups trying to take over Irish Continental say they are being 'severely hampered' by delays in providing detailed and essential financial information about the company.
However, independent ICG directors said they remain committed to working with the consortium so they can progress their possible offer for the benefit of all shareholders.
'Significant and appropriate levels of confidential information and assistance' had been given to Doyle and One Fifty One, they said in a statement.
Cork-based Doyle Shipping and One51 say, however, they are still committed to completing the process with a view towards making a possible offer of at least €20.75 a share.
The two companies began examining the ferries group's books on April 13. They say the delays are happening despite processes put in place with the independent directors to ensure that any information is kept confidential.
Doyle and One51 say they are seeking 'reasonable and adequate disclosure' from ICG to enable the process to be completed.
The approach from Doyle and One51 trumped an earlier offer from a management team led by ICG chief executive Eamonn Rothwell.
