Slovakia's government has lost its majority in parliament after a junior partner withdrew from the four-party coalition.
Foreign Minister Ivan Korcok, Justice Minister Maria Kolikova, and Education Minister Branislav Gröhling -- all from the liberal Freedom and Solidarity (SaS) party -- submitted their resignations on Monday.
The party's leader and former Economy Minister Richard Sulík resigned from his government post last week.
SaS had threatened to leave the coalition after disagreements with populist Finance Minister Igor Matovič.
Matovič's Ordinary People (OĽaNO) party won the 2020 parliamentary election, but he resigned as Prime Minister after acquiring doses of the Russian-made Sputnik V coronavirus vaccine without consulting his coalition partners.
Heger -- a close ally of Matovič and the deputy head of OĽaNO -- became the country's new leader in his place.
Matovič had clashed with Sulík on a number of issues, including how to tackle soaring inflation and high energy prices amid Russia's invasion of Ukraine. He has pushed forward an anti-inflation economic package, that was supported by the opposition far-right Our Slovakia party.
Sulík had also disagreed with the Finance Minister over the country's economic response to the COVID-19 pandemic.
After bitter personal attacks, the SaS had called on Heger to reshuffle his government and remove Matovič from office by the end of August. Heger had indicated that Matovič could resign if his proposed anti-inflation measures were first approved.
“We’re sorry to leave the government,” Sulík told reporters on Monday.
"We will be a constructive but tough opposition," he said, adding that "Matovič is incapable of planning."
Prime Minister Eduard Heger said on Monday that he was planning to introduce candidates for the four empty ministerial posts to Slovakia's President Zuzana Čaputová.
The political uncertainty comes as the Slovak government has been donating arms to the Ukrainian armed forces while opening its border to refugees fleeing the war.
Without SaS, the ruling coalition only holds a minority of 70 seats in the 150-seat Slovakian parliament. A potential no-confidence vote in the minority government could lead to early elections.
Slovakians are not due to go to the polls until February 2024.