BANGKOK, Thailand: Thailand's government is facing its biggest crisis in nearly a year, as Prime Minister Paetongtarn Shinawatra's ruling coalition teeters on the verge of collapse. A leaked phone call with Cambodia's former leader has triggered a political storm, leading a major partner to quit the alliance and fueling calls for her resignation.

The Bhumjaithai Party, the second-largest partner in the coalition, announced its withdrawal late on June 18. It cited damage to national sovereignty and the army's reputation following the leak of a June 15 phone call between Paetongtarn and Cambodia's Hun Sen.

In the audio, Paetongtarn urges Hun Sen to ignore "the other side" in Thailand, including a vocal Thai general who "just wants to look cool." She later describes the remarks as a negotiation tactic.

The departure of Bhumjaithai has left Paetongtarn, 38, with a weakened grip on power. Other allies—the United Thai Nation, Chart Thai Pattana, and the Democrats—were holding emergency meetings this week. If any of them withdraw, her government could be reduced to a minority.

Thai stocks fell as much as 2.4 percent in morning trade, the lowest since April 9.

Police surrounded government headquarters in Bangkok amid protests demanding her resignation. The prime minister, who has yet to comment on Bhumjaithai's exit, was seen entering the complex earlier in the day.

Paetongtarn met top security officials and later told reporters, "We don't have time for infighting. We have to protect our sovereignty. The government is ready to support the military in all ways."

If Paetongtarn resigns, parliament must choose a new leader from the five remaining pre-nominated candidates. Alternatively, she could dissolve parliament and call fresh elections, which could benefit the opposition People's Party.

"The situation yesterday on the leaked phone call is the last straw," said Natthaphong Ruengpanyawut, leader of the People's Party. "I want the prime minister to dissolve parliament... the people want a legitimate government that comes from a democratic process."

Paetongtarn's administration has also faced criticism over the influence of her father, former PM Thaksin Shinawatra, and rising military tension over the Cambodia dispute. This week, the army reaffirmed its loyalty to the Constitution and national unity.