Thai Prime Minister Abhisit Vejjajiva has promised to dissolve parliament next month, meaning a general election will likely be held in late June. But Mr. Abhisit’s insistence on restoring Thailand’s battered democracy has infuriated his backers in the army. They are worried that proxies of former Prime Minister Thaksin Shinawatra will win the election, thus jeopardizing the army’s interests.

Against this backdrop, the military has gone on the political offensive in the past few weeks to intimidate and discredit key opposition figures and institutions. And one of its key tools is the lese-majeste law.

Since becoming army chief in October last year, General Prayuth Chan-ocha has repeatedly stated that the military’s top priority is protecting the monarchy. Under this doctrine, respect for the royal family is the key to the security of the nation. Making this linkage between the palace and the army explicit is designed to guarantee the military’s special role and prerogatives in Thai politics.

Gen. Prayuth recently appeared on national television promising to crack down on anti-monarchy elements, specifically in the pro-Thaksin red-shirt movement. And this was no idle threat. An army officer filed a lese-majeste complaint on behalf of Gen. Prayuth against the opposition Puea Thai MP Jatuporn Prompan and two key red-shirt supporters who allegedly made inappropriate remarks about the monarchy at a rally on July 10.

Gen. Prayuth instructed the Office of the Judge Advocate-General to hand over a recording and transcripts of the allegedly defamatory speeches to the police as evidence. Deputy Police Chief Amnuay Nimmano later stated that the initial examination of Mr. Jatuporn’s speech found “some parts are inappropriate and risk offending the institution (monarchy).” Mr. Jatuporn denies this.

Lese-majeste is defined by Article 112 of the Thai Criminal Code as defaming, insulting or threatening the king, queen, heir apparent or regent, and a complaint can be filed by any citizen. Any charges against Thais are a grave matter. Not only is the penalty of three to 15 years in prison severe, but the investigation and prosecution process is also opaque and grueling. Such charges have been used as a political weapon before, but the number of cases has accelerated sharply in the last few years.

Gen. Prayuth has also warned websites and community radio stations that they will be subject to closer scrutiny for possible lese-majeste content. The Sixth Operation Center within the Internal Security Operations Command, responsible for promoting royal projects, has been urgently tasked to strengthen monitoring work. The Ministry of Information and Communication Technology and the police have also been ordered to take legal action against anyone expressing disloyalty to the royal family.

The military may be exploiting its role as protector of the monarchy to legitimize its own involvement in politics, but in the process it is also further politicizing the institution. The opposition is challenging the coalition of elites which has thwarted the results of the last three general elections. But the pro-Thaksin forces deny that they are anti-monarchy and are using the lese-majeste law to attack their adversaries in the royalist camp.

Mr. Jatuporn has threatened to lodge a lese-majeste complaint against Privy Council President Prem Tinsulanonda, former Prime Minister Anand Panyarachun and Privy Councillor ACM Siddhi Savetsila. Mr. Jatuporn claims that they committed lese majeste during conversations with U.S. Ambassador to Thailand Eric John, based on diplomatic cables released by WikiLeaks.

Mr. Jatuporn’s counterattack against the military raises the political stakes still further. If Mr. Jatuporn indeed files a complaint, Thais do not expect prosecutors would go after Gen. Prem, who has worked closely with the palace. But if the prosecutors decline to bring a case against Gen. Prem, but imprison Mr. Jatuporn, the decision would deepen resentment among the red-shirt supporters, who often complain about the existence of political double standards.

While the military and red-shirt leaders have been tussling, Mr. Thaksin has used this opportunity to step back into the public eye and take the moral high ground. Through his Twitter page, he urged all sides to stop dragging the royal institution into politics for political gain: “I want to plead to all parties to stop doing it—the red shirts, the yellow shirts, political parties and the military. Thailand must stay under a constitutional monarchy. The king is above politics.”

Deputy Prime Minister Suthep Thaugsuban, who is in charge of security affairs, struck back by suggesting to Mr. Thaksin that he take the lead by telling his supporters to stop “inappropriate activities” deemed insulting to the monarchy. But Mr. Thaksin has a point, and it reflects poorly on the state of Thai politics that it took an exiled former leader to state the obvious.

The lese-majeste law is a devastatingly effective political weapon. But the more politicians abuse it, the more they damage the monarchy. In the worst-case scenario, it could become a self-fulfilling accusation. By backing the red shirts into a corner where their criticisms of the elites are accused of being anti-monarchy, the government could split society on the role of the monarchy.

But even if that doesn’t happen, the military’s use of the lese-majeste law could alienate the monarchy from the Thai public, thus reducing the level of reverence which has been carefully built up over decades. It is a powerful way to tear down the royal institution, not safeguard it.