The Office of Fair Trading has pushed back a decision on the proposed merger of AG Barr and Britvic.
Having won the approval of shareholders last week, the merger was due to complete on 31 January.
However, the OFT said it needed more time to complete its review.
In a joint statement, AG Barr and Britvic said regulators had yet to inform them of a revised date, which is expected to come in February. They promised to update the market on the revised timetable in due course.
The merger will result in the creation of a new company to be called Barr Britvic Soft Drinks. To be led by AG Barr CEO Roger White, the company will have a combined turnover of £1.5bn.
Britvic shareholders will own 63% and AG Barr shareholders 37% of the new company.