Hass first came into contact with communist ideas at the Humanities Gymnasium he attended in Stanisławowo,[1] through his association with the left wing of the Związek Polskiej Młodzieży Demokratycznej.

Whilst studying at the Uniwersytet Jana Kazimierza, he became a member of the Union of Independent Socialist Youth,[2] a Marxist, anti-nationalist group that opposed antisemitism.

The exaggerated tirades against Trotskyism performed by Union leader Adam Schaff merely served to pique Hass’s interest.

He then joined an anti-Stalinist group, becoming exposed to critical ideas through Leon Trotsky's dissident publication Byulletin’ Oppozitsii and the Belgian paper Lutte Ouvrière.

On his arrival in Warsaw he astounded a welcoming delegation of students, by announcing that he was a revolutionary who wanted to overthrow the bureaucracy.