Following the Israeli invasion of Lebanon of June 1982, the LCP/PG went underground, participating actively in the formation of the Lebanese National Resistance Front (LNRF) guerrilla alliance in September that year and later joining the LNSF in July 1983. They fought at the 1983–84 Mountain War allied with the Druze People's Liberation Army (PLA) of the Progressive Socialist Party (PSP), Al-Mourabitoun and Syrian Socialist Nationalist Party (SSNP) militias in the Chouf District and at West Beirut against the Christian Lebanese Forces (LF) militia, the Lebanese Army and the Multinational Force in Lebanon (MNF).