The Land Transport Department will start penalising drivers of cars with red licence plates on Sunday if they fail to register with authorities within 60 days.
Department chief Sanit Promwong announced the measure on Saturday, though he did not specify how much the initial fines would be. However, he did say that the penalties would be increased to a maximum of 10,000 baht at the end of this year.
Mr Sanit said the authorities must strictly enforce the regulation because some motorists are known to continue using the red plates as a way to avoid paying road taxes.
He said the red plates are also used to mask the ownership of vehicles used in criminal activities, which further increases the need for the penalties.
The red plates are intended only to be used by new owners during the process of vehicle registration. Once registration is complete, motorists are required to switch to normal white plates.
Authorities allow a two-month window for the registration process, but in response to the abuses, this timeframe will be halved.
Until Dec 31, new vehicle owners must register within 60 days of the day they receive their vehicles from the seller.
In most cases, "the car registration currently takes only one day", Mr Sanit said.
From Jan 1, the Land Transport Department will tighten up the regulation, requiring new owners to register within 30 days.
Violators will be fined up to 10,000 baht under the 1979 Automobile Act for using unregistered cars, Mr Sanit said.
"This stringent enforcement will be in place until a law cancelling the red car licence plates comes into effect," he said.
The department announced in 2015 that it had proposed amendments to the Automobile Act and the 1979 Land Transport Act in order to discontinue the red plates entirely.