Traders outside the parliament building on Rustaveli Avenue were protesting the government's decision to make cash registers mandatory.
The traders, who have been protesting for two weeks, want the registers, which are expensive, to be replaced by a monthly tax paid in lump form.
Inside the building, parliamentarians were due today to discuss an opposition-sponsored motion to delay the implementation of the new regulations, which officially came into force on March 1.
The other demonstration was called to demand that Interior Minister Vano Merabishvili resign over the assassination in January of a bank employee by high-ranking security officials.
Four Interior Ministry officials have been arrested and charged over the murder of 27-year-old Sandro Girgvliani.
The rally is taking place in front of the State Chancellery, which houses the government and the presidential administration.
(Imedi TV, Novosti-Gruziya, Civil Georgia)