The tie-up was referred to the Competition Commission by the Office of Fair Trading last week.
Irn-Bru and Rubicon manufacturer AG Barr has seen more than £60 million wiped off its market capitalisation since the merger was referred.
It closed down 10.5p to 502p, giving it a market capitalisation of £586m.
Britvic has also suffered with around £160m shaved from its market value.
The Fruit Shoot maker ended the day down 8.9p to 395p, giving it a market capitalisation of £962m.
The Competition Commission could take up to six months to report back although both firms have indicated they remain committed to a deal.