Vatican deputy spokesman Ciro Benedettini confirmed to AFP that "summons are being served", adding that an official statement would be made later.
"Vatican magistrates have charged five people at the end of an investigation into the stealing and publishing of confidential Holy See documents," the Repubblica daily said.
Spanish priest Lucio Angel Vallejo Balda and Italian PR expert Francesca Chaouqui were arrested early this month on suspicion of stealing and leaking classified documents to the media.
Vallejo Balda and Chaouqui were both members of a special commission set up by Pope Francis to advise him on economic reform within the Vatican. The fifth person, Nicola Maio, also worked with the now defunct commission.
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Fittipaldi told Italy's ANSA news agency he was stunned by the Vatican's move.
"Maybe I'm naive but I believed they would investigate those I denounced for criminal activity, not the person that revealed the crimes," he said.
The journalist said that under a law introduced in 2013 on the pope's bidding, he and the others risk up to eight years in jail.
The scandal, which has revealed uncontrolled spending by the Vatican as well as accusations of corruption and theft, has awoken painful memories of the last time employees aired the centuries-old institution's dirty laundry.
In 2012, Pope Benedict XVI's butler engineered a series of leaks that revealed fierce infighting in the highest echelons of the Catholic Church and allegations of serious fraud in the running of the city state.
He was sentenced to 18 months in prison, before being pardoned by the pope but banished from the Vatican forever.