Turkey’s largest opposition party is organizing rallies, urging boycotts of pro-government businesses and standing by its presidential candidate — even if he will have to campaign from jail.

At universities, students have formed councils to direct protests and spread the word, sharing tips for dealing with the riot police and tear gas. Their efforts — part of the largest wave of political protest in Turkey in more than a decade — were catalyzed by the government’s March 19 arrest of Ekrem Imamoglu, the mayor of Istanbul and President Recep Tayyip Erdogan’s top political rival.

They have been met with equally vast measures by Mr. Erdogan’s government to quash them. But instead of cowing opposition supporters, the crackdown seems to be energizing them.

“Everybody in the forums and meetings says this is not only about Imamoglu,” said Irem Tacyildiz, 24, an economics student at Middle East Technical University in the capital, Ankara, who has participated in protests. “The fire is already lit.”

But it remains unclear to what extent the nascent protest movement can sustain its momentum and succeed in persuading or forcing the government to change course.

The government removed Mr. Imamoglu from his post and jailed him on Sunday pending trial on corruption charges. That same day, his political party picked him as its candidate in the next presidential election.

His university also annulled his diploma, citing improper procedures more than three decades ago, which effectively blocked him from the presidential race because candidates must have completed higher education.

Mr. Imamoglu has denied the charges and vowed to fight them in court. The opposition has called his arrest a “coup” aimed at blocking a challenge to Mr. Erdogan.

Turkey is officially a democratic republic, but foreign officials, experts and many Turks say that Mr. Erdogan has in recent years pushed the country toward autocracy and is now seeking to further consolidate his power. That means that Turks seeking to resist the government must reckon with Mr. Erdogan’s control of the security forces and influence over the news media and courts, analysts say.

“The authoritarian side is getting stronger and with each step, the areas for struggle where the opposition can express its positions and talk about injustices are becoming narrower,” said Seren Selvin Korkmaz, co-director of IstanPol, an Istanbul-based think tank. “So the opposition always needs to find creative solutions to express their positions to the people.”

The news of Mr. Imamoglu’s arrest led to large nightly protests in front of Istanbul’s City Hall and in other Turkish cities. The police cleared many of them by force.

Leading the opposition is the Republican People’s Party, or C.H.P., to which Mr. Imamoglu belongs. The party of Turkey’s revered founder, Mustafa Kemal Ataturk, it stands for staunchly secular government and draws most its support from the larger, coastal cities.

Its most public face has been its leader, Ozgur Ozel, a pharmacist and lawmaker known for his altercations with members of Mr. Erdogan’s ruling Justice and Development Party in Parliament. After Mr. Imamoglu’s arrest, he took up residence in a room in City Hall with a small bed to coordinate the party’s response, delivering fiery nightly speeches to the protesters.

He called for boycotting companies linked to pro-government news channels that did not air footage of the demonstrations.

“A boycott is coming for whoever ignores this square,” he yelled during an address on Sunday, his voice hoarse. “We will use the power of our consumption.”

In an interview on Friday, Gokhan Gunaydin, a senior official with the party, said it would push for early presidential elections while trying to channel what he called a broader disgruntlement with the “blatant anti-democratic push” by the government.

The party planned to stick with Mr. Imamoglu, he said, even if that meant prison became his “presidential campaign office.”

The party would fight the charges against the mayor, his aides and other party officials and contest the cancellation of his diploma, he said. It would push ahead with the boycott and organize regular rallies to support Mr. Imamoglu around Istanbul and elsewhere in the country.

Many protesters are university students expressing anger at how Mr. Erdogan has run the country and worried about restrictions on civil rights.

At first, the students at her university had been surprised by the harsh police response, said Ms. Tacyildiz, the economics student. So they organized precautions: gas masks, asthma medications and antacids, which can counter the effects of tear gas. A university search and rescue club volunteered to help if protesters got injured.

Many of her friends have been arrested and police were patrolling her campus in plain clothes and using drones to track protests, she said. Some of the protesters wore masks to prevent the police from identifying them.

The students distrust the courts and feel anxious about where the country is headed, she said.

The government has issued blanket bans on public demonstrations and closed transit hubs, and riot police have dispersed protesters with water cannons, tear gas and pepper spray. More than 1,800 people have been arrested and about 260 jailed pending trial, according to the Interior Ministry.

Pro-government news outlets, many owned by allies of Mr. Erdogan, have avoided live broadcasts of the protests while dedicating substantial airtime to the accusations against Mr. Imamoglu.

On Thursday, a parliamentary committee that regulates the news media suspended an opposition broadcaster, SZC TV, for 10 days after accusing it of “inciting the public to hatred and hostility,” according to a statement on its website.

Three other pro-opposition channels were also fined for showing Mr. Ozel, the opposition party leader, criticizing the state prosecutor who ordered the mayor’s arrest, an opposition member of the committee wrote on social media.

Mr. Erdogan has dismissed the protesters as violent vandals and accused the opposition of fueling havoc in the streets to avoid confronting the corruption allegations against its members.

On Thursday, Justice Minister Yilmaz Tunc insisted to reporters that the courts were independent and criticized attempts to dismiss the investigation of Mr. Imamoglu as political.

“This investigation is conducted entirely by independent judicial bodies, and when the investigative authorities become aware of these allegations, it would be unthinkable of them not to open an investigation,” he said.

He denied any relation between Mr. Imamoglu’s nomination to run for president and his detention.

“This is not related to his candidacy process or other developments,” he said.

Turkey’s next election is scheduled for 2028, but many Turks expect Parliament to call for early elections in which Mr. Erdogan, 71, could potentially run against Mr. Imamoglu, 54.

Osman Sert, the director of PanoramaTR, a research institute in Ankara, said Mr. Imamoglu’s arrest had a “rallying around the flag effect” that helped unite the opposition.

Still, he said, it faced a government with great power that would be a challenge to confront.

“Turkey is still not in a position where democracy is already on hold and totally canceled. But these are of course the most difficult days for democracy,” he said. “These are the rules of the game and you can’t get out of it.”