The Justice Ministry has revised the criteria for who is eligible to receive reduced prison terms by royal pardon.
Under the new criteria, those currently incarcerated are now required to have served one-third of their sentence or a minimum of eight years, whichever occurs first, before they can be selected for consideration.
The changes follow criticism over the Department of Corrections' (DoCs) controversial inclusion of convicts in high-profile corruption cases on the list of inmates who had earlier had their terms reduced by royal pardon.
Justice Minister Somsak Thepsuthin said the ministry has acted on recommendations made by an independent committee set up by Prime Minister Prayut Chan-o-cha to look into the matter.
The DoC faced a public outcry last year when it revealed that five high-profile figures in corruption cases including former commerce minister Boonsong Teriyapirom and his deputy Poom Sarapol had received substantial sentence reductions.
Boonsong, who was sentenced to 48 years in jail by the Supreme Court over bogus government-to-government rice deals, has had his term reduced to 10 years and eight months. He will be freed in April 2028.
Poom was sentenced to 36 years by the Supreme Court relating to the same rice deals. He will have his prison term reduced to five years and is due to be released in August 2025.
Gen Prayut appointed an independent committee, headed by Khemchai Chutiwong, a former attorney-general and chair of the committee on national reform in justice affairs, to look into the DoC's criteria for selecting who would receive reduced prison terms.
After receiving the committee report, Gen Prayut instructed the Justice Ministry to act on its recommendations, review the procedure to categorise prisoners and allow prosecutors and judges to take part in the assessment of inmates' behaviour.
Wanlop Nakbua, deputy permanent secretary for justice, said the ministry has followed up on the independent committee's recommendations and reported its progress to the prime minister.
He said the ministry has improved procedures for categorising prisoners and has agreed to take under consideration inmates' criminal behaviour when classifying the prisoners.
He also said that inmates convicted in serious corruption cases will receive fewer benefits as part of improved criteria for granting pardons.
Government's spokesman Thanakorn Wangboonkongchana said the prime minister has asked the public to have confidence in the justice administration system.