The ongoing tussle between the Department of Special Investigation (DSI) and the Senate over alleged collusion during last year’s senatorial election is being viewed as a proxy war between the ruling coalition’s two largest parties.
Observers believe Pheu Thai is backing the DSI in a bid to oust the so-called “blue faction” of senators aligned with Bhumjaithai.
Estimates suggest that as many as 140 of the 200 Senate members are affiliated with Bhumjaithai, the coalition’s second-largest party.
Actions and reactions
Unsuccessful senatorial candidates lodged a petition with the DSI earlier this month, alleging they fell victim to collusion and vote-buying during the election. The plaintiffs turned to the DSI after the Election Commission (EC) made little progress in its investigation.
The DSI says its probe revealed a sophisticated, large-scale operation involving thousands of candidates that helped secure 138 seats in the Senate for pre-selected individuals with political connections.
It found that financial incentives 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 the 138 “chosen” senators, who remain unnamed as of now.
The DSI investigation triggered a backlash from the Senate.
Senate President Mongkol Surasajja insisted last week that all senators had been elected in line with the Constitution, adding that any allegations of electoral fraud or manipulation should be handled by the EC, not the DSI.
Other senators, mainly those linked with the “blue faction”, claim the DSI move is aimed at undermining the Senate and are threatening legal action.
The DSI maintains it has the authority to bring criminal charges against the 138 senators under suspicion.
However, to continue with the case, it needs approval from its 22-member board for special cases, which is chaired by Pheu Thai’s Deputy PM Phumtham Wechayachai and includes Justice Minister Tawee Sodsong and top bureaucrats from several ministries and state agencies.
The board postponed its meeting on the matter from Tuesday (February 25) to March 6, citing the need for more input from the EC chief.
Senators’ many powers
The current 200-strong Senate enjoys a wide range of powers – though its authority to participate in voting for a new prime minister expired last year.
Senators can, however, vote on constitutional amendments and other legislative bills, approve nominations to independent agencies such as EC commissioners and Constitutional Court judges, and scrutinise the government’s performance through interpellations and non-voting 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.
It also needs a simple majority from both Houses combined, or at least 351 votes in favour from the 500 MPs and 200 senators in its first and final readings, when the bill also requires approval from at least 20% of opposition MPs.
The current charter empowers the Senate to approve appointees of several independent agencies and organisations, before they receive final endorsement from the King.
These officials include election commissioners, members of the National Anti-Corruption Commission (NACC), Supreme Administrative Court judges, Constitutional Court judges, National Human Rights Commission members, the attorney-general and the Council of State’s secretary-general.
Sights set on the next election
This year, four of the six election commissioners will complete their seven-year tenure, including EC chairman Ittiporn Boonpracong. The EC chief and one other will retire in August and the other two in December.
The process to select their successors is expected to kick off later this year, with the Senate expected to play a key role in the new appointments.
Analysts point out that political control of the Senate – whose wide-ranging powers include approving EC nominees – could be crucial to success in the 2027 election.
Since kicking off their five-year tenure last July, the latest crop of senators has proved they are a political power to reckon with. Dominated by Bhumjaithai-linked individuals, the Senate recently blocked efforts by Pheu Thai and the opposition-leading People’s Party to amend the Constitution to pave the way for a charter rewrite.
The “blue” senators mirrored the stance of Bhumjaithai MPs, who staged a walkout during parliamentary deliberation of the proposed amendments to stall their passage.
Analysts believe that Pheu Thai leaders fear these senators could further sabotage their political moves and realise that something needs to be done to change the tide.
They say the DSI is being used as a political tool in this ongoing power struggle. The case against the 138 senators could end in them shifting their allegiance or being disqualified, opening the way for new senators loyal to the rival party.









