A woman member of the ruling PRO party — of Governor María Eugenia Vidal and President Mauricio Macri — reported Mosca to police for allegedly sexual assaulting her.
Mosca's absence from the chamber leaves it under the control of Peronist lawmaker Marisol Merquel, as speaker, and Kirchnerite lawmaker Carlos Moreno, as vice-speaker.
A request to strip Mosca of his parliamentary immunity is also moving through Committee Level in the Legislature.
The legal case is in the hands of the Eighth Civil Court of Judge Félix Igarzábal, in Buenos Aires City, where the woman lives. The case will also be assessed in a criminal court in Mar del Plata, where the incidents allegedly took place.
It is the second high-profile case of its type in Buenos Aires province's Congress, amid a wave of allegations late last year about sexual abuse and violence committed against woman by men in positions of power.
Kirchnerite senator Jorge 'Loco' Romero also faces court proceedings for the alleged assault on Stephanie Calo, a fellow member of the La Cámpora youth movement led by national lawmaker Máximo Kirchner.
Romero recognised having demonstrated "chauvinistic behaviours" but denied any sexual assault against Calo.