A proposed £1.4 billion merger between the maker of Robinsons and the owner of Irn-Bru is facing uncertainty after a key investor reportedly hit out at the terms of the deal.
Britvic, whose brands include Robinsons and Tango, has been in talks with AG Barr, the maker of Irn-Bru, to create a soft drinks powerhouse.
Harris Associates, Britvic's eighth-biggest shareholder with 3.4%, has criticised the "poorly negotiated" share ratio under the terms of the deal, The Sunday Times said.
AG Barr approached its bigger competitor in September after Britvic's summer was hit by poor weather conditions and a costly recall of its Fruit Shoot product.
Britvic shareholders would take 63% of the newly-formed group under the proposed terms being discussed, while AG Barr investors would get 37%.
But analysts have said the deal values Britvic at only 1.7 times AG Barr, when its operating profits and revenues are several times higher.
David Herro, chief investment officer for international equities at Harris, told The Sunday Times: "The share ratio was poorly negotiated in our view, and it has not been properly explained as to how the companies came up with that ratio."
The two firms have twice extended the deadline by which a formal announcement must be made.
Takeover Panel rules mean the boards are restricted in what they can tell shareholders about benefits and cost savings until then - but analysts believe the deal could bring savings of around £45 million a year.
The deadline now falls on November 28, the day Britvic is due to update the market with its annual results.