The National Human Rights Commission (NHRC) has expressed strong opposition to its proposed merger with the Office of the Ombudsman.
The Office of the Ombudsman backs the merger.
Ombudsman Siracha Vongsarayankura said he has no objection to the merger because he thinks the office's powers will remain the same.
Both bodies can help the public, and their roles are supportive of one another, he said.
But on Wednesday, the human rights agency spoke out against the merger, proposed by the Constitution Drafting Committee (CDC).
The CDC claims the merger will boost the agencies' efficiency and allow them to help the public better.
The NHRC, however, says it has different authority and work objectives from the Office of the Ombudsman, and merging the two would not make for a happy marriage.
The NHRC's key duty is to promote and protect people's human rights based on the constitution and laws, it said. It is also responsible for promoting equality.
The Ombudsman's main duty, however, is holding state officials accountable and helping people gain access to justice and fairness — but these cases are not necessarily related to human rights.
The proposed merger would force the NHRC and Ombudsman to play roles without the appropriate expertise.
The NHRC disagreed with the CDC's reasoning the merger would empower the human rights agency to report concerns to parliament directly.
It can already do this under the current laws, the NHRC said.
The merger would reduce people's opportunities to seek expertise from the NHRC and stop the agency from focusing on their problems.
The merger would also bring about changes in rules and regulations concerning the agencies, which could lead to conflicts over personnel and budget management, it said.
Meanwhile, the Assembly of the Poor condemned the proposed merger.
"The NHRC is important and necessary for the protection of people's rights, particularly for the poor," the group said.
Also on Wednesday, Asean Parliamentarians for Human Rights (APHR) also expressed deep concern about the merger proposal day.
The proposal undermines the independence, efficiency and authority of the NHRC, the group said.
"The plan appears to have no purpose other than to weaken the NHRC's ability to seek justice on behalf of those whose human rights have been violated,'' it said.
"It is also notable and regrettable the decision was made without any apparent consultation with civil society or human rights defenders in Thailand," APHR said.
Bowornsak Uwanno, head of the CDC, announced on Saturday the charter drafters had agreed to merge the NHRC and the Office of the Ombudsman into one organisation.
The new name of the merged agencies will be the Office of the Ombudsman and Human Rights Protection.
The state agencies have similar functions and the merger is intended to increase their ability to provide human rights protection, Mr Bowornsak said.