The operation, based in Istanbul, was launched across eight provinces, said the source, who asked not to be named due to restrictions on talking to the media.
Istanbul's Chief Public Prosecutor had issued arrest warrants for 189 lawyers on charges of being members of an armed terrorist organization.
Some are also accused of having the ByLock cellphone application, which is said to have been used by members of FETO.
Operations are ongoing to apprehend the remaining suspects.
FETO, led by U.S.-based Fetullah Gulen, has been accused of orchestrating the defeated coup of July 2016 that left at least 248 people martyred, and around 2,200 others wounded.
ByLock is said to have been exclusively used by the group's supporters until it was reportedly cracked by the security forces, which allowed the identification of FETO members.
Since the failed coup, tens of thousands of police officers, military service personnel and other public employees have been arrested over their alleged ties to FETO.
