From then on, smoking will be banned in all public places, including hotels and restaurants except where they have installed special isolated smoking rooms.
Even then, patrons will not be able to enjoy a coffee and cigarette as the rooms are reserved exclusively for smoking, and all food and drink will be served in the common non-smoking area.
The sale of tobacco products to teenagers under 18 will also be banned.
Under the new legislation, if a restaurant or pub does not have a proper smoking room, customers will have to go outside to light up or face a fine of 125 euros (170 dollars) for smoking indoors.
Ventilated glass cabins can also be installed in the workplace and some public institutions, but like the smoking rooms they will be reserved for smoking, with no eating or drinking allowed inside.
Most public institutions and restaurants "have prepared for the implementation of the law by completely banning smoking indoors. Employees will have to smoke in the open air," the daily Delo reported on Friday.
Smoking in Slovenia was allowed until now in specially marked public areas, but with no physical partition between smoking and non-smoking areas.
The new law to crack down on smoking also increased the minimum legal age for buying cigarettes and other tobacco products to 18, from 15 at the moment.
Merchants will also be authorised to ask for identification to check the age of young tobacco buyers.