Explainer: How the Senate became a battleground for Thailand’s political future

What began as a battle for control of the Senate between the ruling coalition’s largest parties, Pheu Thai and Bhumjaithai, has turned into a conflict that threatens to reshape Thailand’s political landscape.

The Department of Special Investigation (DSI) has accused over 100 senators linked with Bhumjaithai of laundering money for an alleged vote-rigging scheme in last year’s Upper House election.

The DSI comes under the authority of Justice Minister Tawee Sodsong, leader of the Prachachat Party and also considered an ally of Pheu Thai.

The row is eroding the government’s stability, as Pheu Thai and Bhumjaithai trade blows in a tit-for-tat dispute. Analysts predict it will culminate in Bhumjaithai’s expulsion from government.

Left with a smaller coalition and a slim majority, Pheu Thai is expected to dissolve the House to pave the way for a new election.

If the accused are found guilty of operating a vote-rigging scheme, half of the Senate could lose their seats. Or, the Senate election may be declared invalid, leaving the entire Upper House vacated.

Moreover, the multiple allegations stemming from the Senate vote include claims that Bhumjaithai undermined the country’s constitutional monarchy by colluding in vote-rigging – an accusation that could lead to the party’s dissolution.

Tainted election

Last year’s senatorial vote saw candidates allied with major political parties – including Pheu Thai, Bhumjaithai, and Move Forward (predecessor of the opposition People’s Party) – contesting for the 200 Upper House seats.

The election, which saw over 40,000 candidates vote among themselves during multiple rounds at district, provincial and national levels to determine the final winners, was marred by allegations of fraud and manipulation.

Observers agreed that while all major parties plotted to get their allied candidates elected, Bhumjaithai was easily the most successful. Estimates suggest that up to 130 Senate seats are held by so-called “blue senators”, named for Bhumjaithai’s colours.

Unsuccessful senatorial candidates filed a complaint with the DSI in February, alleging they were victims of collusion and vote-buying during the election. The plaintiffs turned to the DSI after the Election Commission (EC)’s investigation seemingly stalled.

The DSI said its own probe revealed a sophisticated, large-scale operation involving thousands of candidates that helped secure 138 Senate seats for pre-selected individuals with political connections.

It found that bribes were offered in exchange for votes during the six rounds of voting between June and July last year. The discovery led to charges of criminal association and money laundering against 138 senators.

Senators summoned

Several senators have decried the DSI’s involvement in the case, insisting that the EC has sole jurisdiction. The EC eventually accused 55 senators of vote-rigging, including Senate president Mongkol Surasajja and first vice-president General Kriangkrai Srirak.

The poll agency also welcomed the DSI’s support, explaining it needed help unravelling the complex money trail at the heart of the vote-buying scheme.

The DSI used artificial intelligence (AI) technology to analyse the huge amount of information and evidence collected.

Justice Minister Tawee confirmed the EC was mainly handling the vote-rigging charges while the DSI focused on the money-laundering aspect of the case.

The 55 senators were called to EC headquarters in three groups between Monday (May 19) and Wednesday (May 21) to acknowledge charges against them.

Some of the suspects were unhappy that the summonses were delivered to their homes by DSI officers, although the agency insisted the move had been approved by the EC.

The decision to use law enforcement agents to deliver the summons was widely seen as an attempt to amplify the case against the targeted senators.

Former election commissioner Somchai Srisutthiyakorn said it was unusual for the EC to tip off media outlets about summons delivery to suspects’ houses, adding that such documents are normally sent by registered mail.

Somchai noted that the EC has no authority to issue arrest warrants against individuals who fail to respond to summons. However, he urged the senators to show up and explain themselves to the EC, saying this would benefit their cause.

Tit for tat

The case suffered a setback last Wednesday (May 14) when the Constitutional Court suspended Tawee from overseeing the DSI and serving as deputy chair of its special cases committee, pending a verdict on whether he abused his authority by endorsing the DSI investigation. The DSI said the court order would not affect its investigation.

Tawee’s suspension was a big blow for the Pheu Thai camp, although its Deputy Prime Minister Phumtham Wechayachai will continue to oversee the Justice Ministry after the court found no evidence to justify his suspension.

The suspension stemmed from a complaint lodged by 92 senators with the Constitutional Court in March, seeking the removal of Phumtham and Tawee from their posts for allegedly interfering in the Senate election by permitting the DSI probe.

Last Friday (May 16), a rival group of senators petitioned the Senate president to seek a Constitutional Court ruling on whether the 138 suspects should be suspended from duty.

The petition coincided with a move by lawyer Natthaporn Toprayoon, a former adviser to the Ombudsman, to file a complaint with the EC against Bhumjaithai. He accused the party of undermining the country’s political system by colluding in vote-rigging, and called for its disbandment and political bans for its executives.

Locking horns

Already embroiled in conflict over constitutional amendments and the casino entertainment complex bill, Pheu Thai and Bhumjaithai now appear to be locked in battle for control of the Senate, whose wide-ranging powers include ratifying appointments to powerful independent agencies such as the EC and Constitutional Court. Analysts point out that control of the Upper House could be crucial to success in the 2027 election.

The Senate’s many powers also include voting on constitutional amendments and other legislative bills and scrutinising the government’s performance through interpellations and general debates.

Any bill to amend the Constitution requires support from at least one-third of the Senate, or 67 senators, to pass its first reading. In the first and final readings, it also needs a simple majority from both Houses combined, or at least 351 votes from the 500 MPs and 200 senators.

The current charter empowers the Senate to ratify appointees of various independent agencies before they receive final endorsement from the King.

These include election commissioners, members of the NACC, Supreme Administrative Court judges, Constitutional Court judges, National Human Rights Commission members, the attorney-general, and the Council of State’s secretary-general.