The Police National Fraud Investigation Unit raided the house of the prime minister's secretary, Shula Zaken, and the houses of seniors at the Israel Tax Authority and other suspects.
Zaken is suspected of having been involved in the appointment of civil service senior officials, and of taking advantage of this to grant tax benefits to her cronies.
The investigation was revealed on Channel 10 Monday evening.
On Tuesday, 25 suspects were brought in for investigation at the Fraud Unit headquarters.
The Fraud Unit has been conducting a wide-scale secret investigation against civil service officials recently, in light of suspicions they were involved in various corruption-related offenses.
The police are probing, among others, senior Tax Authority officials, private businessmen and other interested parties.
The police suspect that head of the Tax Authority, Jacky Matza, was also involved in the affair.