In 1980, 13 members of Parliament published a letter criticising Mobutu's regime and were arrested for "aggravated treason". Lihau testified on their behalf during the ensuing trial. Two years later he joined them in founding the Union pour la Démocratie et le Progrès Social (UDPS) as an opposition party to Mobutu; Lihau soon became the new party's president. Mobutu was particularly disturbed by Lihau's membership in the party since, as a native of Équateur Province, he added to the geographic diversity of the organisation and therefore its political clout. In retaliation, Mobutu incarcerated him, suspended his rights, confiscated his personal property, and eventually banished him to the village of Yamake in Équateur Province. In August 1983, Lihau joined several of his colleagues in attempting to interrupt a meeting between government officials and United States Congressmen at the Hotel InterContinental in Kinshasa while wearing Western suits and ties (then banned by Mobutu). A violent struggle between the UDPS members and Mobutu's security police ensued in full view of the American delegation and received a great amount of media attention in the United States.
