"Let's unite, let's be as many as possible, even if we have to return to the roundabouts," said Communist Party leader Fabien Roussel, a reference to the "Yellow Vests" movement starting in 2018 that had anti-government protesters gather at busy traffic circles.
Unions representing the RATP's nearly 70,000 employees say they are feeling the pinch of soaring prices, but are also overstretched because of insufficient hiring, resulting in increased sick leave.
That has led to more service delays or lower frequency on busy metro lines in recent months, causing headaches for the system's roughly 12 million daily users.
In neighbouring Spain, meanwhile, an association of independent truck drivers called for an unlimited strike starting Monday to protest against delays in the implementation of a charter protecting their incomes.