The rightwing premier, who refused to resign and vehemently defended his aides, has been summoned for crisis talks later today by his leftist rival President Milos Zeman.
The scandal erupted when police swooped down overnight Wednesday and yesterday on the cabinet office and the defence ministry as well as a bank, a villa and several offices of businessmen with ties to Necas's party.
Jana Nagyova, head of Necas's office, was charged with complicity in the "abuse of power and with bribery," deputy chief prosecutor Pavel Komar told reporters today.
The Czech CTK news agency today quoted a high-profile lawyer as saying Nagyova had asked his client, a former military intelligence head, to tail Necas's wife Radka late last year.
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Necas announced he was getting divorced earlier this week.
Ironically, Necas, a 48-year-old physicist, has made a high-profile anti-corruption drive a centrepiece of his administration, in power since July 2010.
His shaky minority governing coalition has so far survived eight confidence votes, but fresh polls show the leftwing opposition is poised to win the next election due in May 2014.
Robert Slachta, chief of the UOOZ anti-organised crime unit, said today that 400 policemen were involved in what is the largest anti-graft raid the corruption-prone Czech Republic has ever seen.
"The police performed 31 searches and seized USD 6.2-7.8 million and dozens of kilograms of gold," Slachta said.
Prosecutors have also charged two former lawmakers from Necas's party -- Ivan Fuksa and Petr Tluchor -- with bribery, and suggested today that their ex-colleague Marek Snajdr would be charged too.