Direct university entrance exams will take place over a shorter given period to prevent applicants "shopping around" and make places available to more students.
Somkid Lertpaithoon, who chairs the Council of University Rectors, said the council has resolved that for the next academic year, all direct entry exams will take place in January.
Universities have typically held these exams at a time of their own choosing.
Some universities hold their exams months apart, allowing applicants, especially those from rich families who can afford the exam fees, plenty of time to prepare and sit many tests.
In most cases, applicants pass the tests and are offered places by several universities. Since they can only choose one university they have to turn down other places offered to them.
The practice is widely seen as unfair on students unable to sit an exam because of a lack of exam slots and who may otherwise have won a place if they had taken the test.
Mr Somkid said the council hopes that by holding direct entry exams only in January it will discourage applicants from "shopping around".
With exams scheduled closer together, the applicants will have less time to prepare for them. Some university entrance exams will likely take place on the same date, he said.
Mr Somkid said the council believes this will reduce the number of multi-exam sitters.
Mr Somkid denied allegations some universities deliberately set the dates of their exams far apart to make money from exam fees.
He said organising tests incurs a lot of expenses and does not make universities rich.