A demonstration is due to take place in Ayr's Wellington Square at 1pm with social networking sites encouraging people to go along and "protect our British rights to fly our union flag". Protesters also gathered at Livingston's Civic Centre on Thursday night.
In Glasgow, police are gearing up for a protest in today at midday, which clashes with a republican march through the city. Officers will also be in place for a gathering in Kirkcaldy in Fife at 7pm on Sunday.
Anti-sectarian campaigners have already called for groups to ensure their protest is peaceful.
The flag decision in Belfast has already resulted in violence in the Northern Irish city, including the attempted murder of a police officer whose patrol car was petrol bombed.
Nil By Mouth campaign director Dave Scott said: "We urge those involved to make their point in a peaceful, dignified fashion."
The protests are being organised through Facebook. A page promoting the Ayr protest said: "Please come support us to protect our British rights to fly our union flag, this is a peaceful protest so bring the family along, and don't forget your union flags folks."
South Ayrshire Council said it had received no notice of the protest.
Strathclyde Police said: "We are aware of the Facebook page and planned protest, which, if it goes ahead, will be policed appropriately."