Private equity firms Carlyle Group and Pacific Equity Partners have lifted their buyout proposal for Link Group to $5.40 per share from $5.20, and also threatened to walk away from the deal if they are not granted access to Link's inner workings by 5pm on Wednesday.

The revised proposal comes after Link on October 23 dismissed Carlyle and PEP's initial $5.20 a share approach as "materially" undervaluing the group.