The Moroccan plaintiffs said in a statement that "criminal intrusion" into their phones had caused "serious harm, due to (our) activities as human rights defenders, journalists, lawyers and politicians."
Claiming that they were "victims of illegal intrusion into their phones by Pegasus software", they said they are planning to file a joint complaint under a case brought by messaging service WhatsApp, which accuses NSO of allowing mass espionage against activists and journalists.
"These practices must stop immediately," lawyer Fouad Abdelmoumni told AFP.
"Pegasus has been used to crush human rights activists, political dissidents, journalists and lawyers. This is unacceptable."
Those filing the complaint include three rights activists and the wife of jailed dissident journalist Soulaimane Raissouni, who is serving a five-year sentence on sexual abuse charges.
Pegasus gives government users near-complete access to a target's device, including personal data and messages, photos, location and even the camera.
The US Supreme Court in January gave a California federal court a green light to hear the case, throwing out an NSO appeal.
WhatsApp accuses NSO of targeting some 1,400 devices with spyware to steal information.
Amnesty International in July 2021 accused several governments, including Morocco, of using the technology against political dissidents.
Morocco has repeatedly rejected the accusations.
The head of the country's CNDP data protection agency said Wednesday that people "shouldn't be duped by a few gesticulations by non-specialists."
"The 'accusers' should justify their statements scientifically, avoiding media assassination attempts," Omar Seghrouchni tweeted.
Ali Reda Ziane, the son of a jailed lawyer and one of the plaintiffs, said that "even if Morocco denies being a customer of NSO, the Israeli government says it has provided the software to the Moroccan regime."
"If that's true, NSO is an integral part of Morocco's repressive apparatus," he said.
Spanish journalist and Morocco expert Ignacio Cembrero has also publicly accused Rabat of hacking his phone, after a pro-government Moroccan news outlet published private WhatsApp messages between him and Spanish officials.
Rabat quickly sued him, demanding he withdraw his allegations and pay legal costs.
A Spanish court is set to rule on the case in the coming weeks.
Morocco has taken similar steps in France over claims it used Pegasus software to spy on journalists and politicians, among them President Emmanuel Macron.