PHNOM PENH, Cambodia — High on a Cambodian cliff, the Preah Vihear temple has weathered war and territorial disputes. Now it’s at the center of a political tug-of-war in neighboring Thailand.

As it has over the centuries, the ancient temple is fueling nationalist sentiment on both sides of the border, and opposition supporters in the Thai parliament are raising it as a reason for why the prime minister should step down.

Thai prime minister, Samak Sundaravej, last week endorsed Cambodia’s bid to register the temple as a UNESCO World Heritage site — enraging opposition lawmakers who say he is yielding national sovereignty to Cambodia.

Never mind that the International Court of Justice awarded the temple and the land it stands on to Cambodia in 1962 — it remains an issue in both countries.

“The Preah Vihear temple is part of a wounded history of Thailand and Cambodia,” a historian at Bangkok’s Thammasat University, Charnvit Kasetsiri, said. “It was used to stir up a nationalist movement during World War II, and again during the Cold War … and is now threatening to inflame politics again.”

The crumbling stone temple, which is a few hundred feet from Thailand’s eastern border with Cambodia, is the centerpiece of a no-confidence motion against Mr. Samak. The opposition accuses the prime minister of policy mistakes and of being a proxy for deposed leader Thaksin Shinawatra.

“Preah Vihear is the knockout punch” that could bring down Mr. Samak, the opposition leader, Abhisit Vejjajiva, told Parliament. However, Mr. Samak’s ruling coalition has an overwhelming majority, and he is expected to easily survive Friday’s vote.