ATHENS — The thunder rumbling over the Acropolis as winter storms barreled down on Greece on Thursday may pale in comparison to the clamor expected to erupt  in parliament as a wiretapping scandal dubbed “the Greek Watergate” comes to a head. 

Last summer Greece’s main opposition party, the leftist Syriza, accused the prime minister, Kyriakos Mitsotakis, of orchestrating unauthorized electronic surveillance of  high-profile political opponents. This week his predecessor, Alexis Tsipras, submitted a censure motion against Mr. Mitsotakis’s conservative government that  will come to a vote on Friday.

There is little doubt that the vote will be a contentious one, with the seeds of discord planted early when it emerged in August that a cellphone belonging to another opposition politician, Nikos Androulakis, had been bugged using Predator spyware. 

Mr. Androulakis, leader of the influential Greek socialist party Pasok, said that the national intelligence service, EYP, surveilled his conversations in 2021. He subsequently filed a complaint in Greece’s highest court. While Mr. Mitsotakis said the wiretaps were “a huge and unforgivable mistake,” he has maintained that all the surveillance was conducted legally. 

Greek government officials have denied there was any intentional wiretapping of anyone. Furthermore, in December legislation was passed to initiate reforms of the EYP and separately to ban the sale of spyware. That followed a detailed report in a leftist newspaper that more than 30 Greek ministers, government officials, and journalists had been unknowingly subjected to surveillance by means of malware on their mobile phones.

The initial Predator spyware case, which has also crossed the radar of EU headquarters at Brussels, remains under investigation by prosecutors, but that did not stop the momentum for greater accountability that preceded Mr. Tsipras’s political gambit on Wednesday.

Mr. Mitsotakis’s center-right New Democracy party holds a majority in parliament, albeit a thin one, with 156 deputies in the 300-seat body. So it is unlikely that what amounts to a call for no-confidence in the government will pass. Yet with Greece in pre-election mode ahead of parliamentary elections expected in the spring, the risk for Mr. Mitostakis is if the imbalance in polls starts to tilt in Syriza’s favor. 

Greece’s SKAI television has reported that according to the first major poll in 2023, which was conducted between January 19 and 23, New Democracy held a lead of 7.5 points over opposition Syriza. Also in that poll, Mr. Mitsotakis was called the most suitable prime minister by 38 percent of respondents, against 27 percent who said that Mr. Tsipras would be best suited for the office. 

The combustible atmosphere at Athens could shake up those numbers. That is especially so because Messrs. Mitsotakis and Tsipras are longtime and formidable rivals, each with unique political pedigrees in a country that is not only a huge magnet for tourism and culture but is arguably America’s most important strategic ally and NATO partner in the eastern Mediterranean. Mr. Tsipras served as prime minister between 2015 and 2019, when Greece was reeling from financial crisis;  the austerity measures he imposed at the behest of international lenders, chief among which Germany, were not universally lauded. 

Mr. Mitsotakis is a scion of one of the best-known political families in Greece. His father, Konstantinos, served as the seventh Greek prime minister, between 1990 and 1993. He is the face of the establishment, but in today’s fractious political environment longevity is not assured. On learning of the opposition’s maneuver at Athens while he was in Crete, Mr. Mitsotakis said, “Mr. Tsipras wrote the preface of his defeat by himself by filing a motion of no confidence,” adding that “this will turn into a motion of his own disloyalty” to the Greek people.

If in 2023 Greece is faring better economically than it has in previous years, the Greek Watergate has almost been a gift to the opposition, with Syriza doing its best to leverage a sense among large segments of Greek society that New Democracy has an elitist drift that puts it out of touch with quotidian concerns like high energy prices and stubbornly low wages.  

Adding to the government’s woes are reports of intimidation of the head of the Communications Privacy Protection Authority, or ADAE, Christo Rammos. The newspaper To Pontiki reported that New Democracy’s attempt to link Mr. Rammos to the opposition Syriza party “has caused a particularly bad impression on the public, who supported Kyriakos Mitsotakis as a pro-European politician.”

This week, after Mr. Tsipras saw the conclusions of the ADAE, he told parliament that “for the past six months, Greek society has been witness to disclosures of an inconceivable number of phone taps, the deepest deviation from rule of law that the country has seen in its modern history.”

According to that report, Mr. Tsipras said that at one point the minister of energy and even the powerful Greek army chief, Konstantinos Floros, had been wiretapped. In the meantime, with New Democracy accusing the opposition of defamation and Friday’s vote looming, Greek media were reporting that a European Parliament commission of inquiry, called PEGA, has quietly been urging Athens to resolve the wiretapping controversy before the country goes to elections.

For now, the main actors in this drama are all Greek. Even if the protagonists are Messrs. Mitsotakis and Tsipras, the cast of characters is widening ahead of Friday’s showdown. Two former prime ministers, Antonis Samaras and Kostas Karamanlis, have publicly disagreed with the government’s handling of the scandal — and, worryingly for Mr. Mitsotakis, both are members of his New Democracy party.