Acting president Viv Pearce expressed fears on Thursday that school canteens would suffer financially under the changes and needed a longer transition period as well as a detailed school education program.

"The big problem has been with the college canteens, where if you just remove things off the shelf, so to speak, the kids will just go across the road to fast food to buy sugary drinks and at the same time the unhealthy food," she told ABC radio.

Chief Minister Katy Gallagher responded by saying she would not be swayed and schools had been given sufficient warning of the changes.

"I'm not convinced of the need to delay. We have announced a ban and the ban had a full school year to run. Many schools already don't sell soft drinks, particularly the primary schools," Ms Gallagher said.

NSW and Victoria already have bans on sugary drinks, which were brought in as early as 2006.

"The longer we delay it, it pushes it out, and we continue to have a model which supposedly means the financial viability of canteens is underpinned by selling a product that is causing harm to children, and I think we need to draw a line in the sand," Ms Gallagher said.

Ms Pearce said she was "very supportive" of the government's efforts concerning healthy food and sugary drinks, but many school canteens across Canberra have expressed their fears the ban will result in them going broke.

"You want school canteens to be the place kids want to hang out," she said.

Ms Gallagher brought forward a five-year phase-out of sugary drinks in territory schools in February as part of tough measures to tackle the ACT's alarming rate of childhood obesity.

The ban on the sale of fruit juice and soft drinks from vending machines at Canberra public schools was put in place in term 1.