If such dealers are not allowed to sell gas, rural customers in particular may face immense difficulties by being forced to go longer distances to buy from larger dealers.
Consumer minister Bandula Gunawardane says the Consumer Affairs Authority (CAA) will make the rule effective from December 01.
Liquefied Petroleum (LP) gas which is retailed in Sri Lanka by Shell Gas, and Laugfs, a local firm, is supposed to have 12.
5 kilograms of gas.
But there have been accusations that some dealers were siphoning off gas before selling.
Shell had also devised a shrink wrap seal to counter the problem.
Especially in rural areas gas cylinders are sometimes re-sold by small shopkeepers who buy from main dealers.
Officials say they are not aware of how many LP gas dealers were in existence.
Trade secretary R M K Ratnayake says small dealers who sell between 10 to 15 cylinders a month may have difficulties in buying a scale.
An Avery branded scale which could be used to weigh