Transport Minister Saksayam Chidchob explained that only cars with maximum capacity of seven people would be eligible for registration.
The draft ministerial regulation was drawn up to serve the ride-hailing market via apps such as Grab.
Currently, taxi drivers are required to have a public-vehicle licence, but many drivers in the call-taxi business only have a personal licence.
The ministerial regulation aims to close this loophole and legalise all cars operating in the call-taxi business.