Among those arrested in Istanbul on Saturday and the neighbouring province of Tekirdag and the capital, Ankara, were senior officials from Istanbul Metropolitan Municipality, local media reported.
The March 19 detention of Istanbul Mayor Ekrem Imamoglu, who is the main challenger to President Recep Tayyip Erdogan's 22-year rule, saw hundreds of thousands of people flood the streets of Turkish cities to protest what many consider a politically motivated case.
The government insists Turkey's judicial system is independent.
In a statement, the Istanbul Chief Public Prosecutor's Office said simultaneous operations were conducted against 53 suspects, six of whom remain at large.
Searches were continuing at homes and workplaces, it added.
Demonstrations against Imamoglu's jailing and wider democratic backsliding saw more than 2000 people arrested for taking part in banned protests last month.
Many of them were students but journalists and trades unionists were also among the detainees.
Imamoglu, who also faces terror-related charges in a parallel investigation launched last month, was nominated the presidential candidate for his Republican People's Party, or CHP, while in prison.
Elections are due in 2028 but could come earlier.
The cases against him, which include several others that pre-date the March investigations, could see him banned from politics.
The CHP-supporting Cumhuriyet newspaper reported that Saturday's arrests included the deputy secretary general of Istanbul municipality, Imamoglu's private secretary and the head of the city's water company.
Gokhan Gunaydin, a senior CHP lawmaker, said the municipality was being "effectively rendered inoperable" by the arrests.
The wife of Imamoglu's adviser was also detained on Saturday.
The adviser was among some 100 arrested in March's wave of arrests and remains in prison.
Demonstrations against what the opposition calls the "March 19 coup" are continuing, although on a smaller scale.
Ankara governor's office said on Saturday that 30 people were arrested at a protest the previous evening.
The CHP was due to hold a rally later on Saturday in the Mediterranean city of Mersin.
The party won a swath of major cities in 2019 local elections, making further gains in last year's polls.
In Istanbul, Imamoglu's victory ended 25 years of control for Erdogan's party and its predecessors.
