Prosecutors summoned the four women for questioning on Wednesday following complaints from Nation’s Future.
Mada Masr said they were later released on bail on charges including publishing false news and defaming party members.
Free speech and press freedom in Egypt have been significantly curtailed under President Abdul Fattah al-Sisi.
Madr Masr is one of the few remaining Egyptian media outlets that are not under direct state control or influenced by the government, according to the global media watchdog Reporters Without Borders (RSF).
On 31 August, Madr Masr published a newsletter about Nation’s Future, which dominates parliament and strongly backs President Sisi.
The article said an inquiry had implicated senior officials in Nation’s Future in “grave financial violations” and that this was expected to “lead to their departure from the political scene”.
Nation’s Future denied the story “in its entirety” and accused Madr Masr of using “dubious and unprofessional tactics to destabilise the country’s security”.
Dozens of legal complaints were filed by party members against the three journalists whose bylines were on the article – Rana Mamdouh, Sara Seif Eddin and Beesan Kassab – along with their editor-in-chef, Lina Attalah.
On Wednesday, the women were questioned by prosecutors in Cairo and then informed they were being charged with slander and defamation of Nation’s Future members, using social media to harass party members, and publishing false news intended to disturb the public peace, Mada Masr reported.
Ms Attalah was also charged with operating a news website without a licence.
Madr Masr has been trying to obtain a licence since 2018, when a new law regulating the media came into force.
The outlet said on Saturday that was confident “in the integrity of our legal position and our commitment to the highest professional publishing standards”.
“We also express our regret that the majority political party in Egypt, known to be proximate to power, is using such tactics to intimidate a press outlet that is operating on behalf of public interest,” it added.
RSF said it was extremely concerned by the threat to Madr Masr and warned that “the constant harassment, intimidation and arrests of journalists by Egypt’s government are reaching dangerous heights”.
