During the 1905 general strike, Haapalainen was one of the leading Red Guard organizers in Helsinki. A year later, he was the delegate of the Finnish Social Democratic Party at the 4th Congress of the Russian Social Democratic Labour Party in Stockholm. In the summer of 1906, Haapalainen represented Finnish Social Democrats in the underground Bolshevik committee planning the Sveaborg rebellion. In April 1907, Haapalainen was elected as the first chairman of the Finnish Trade Union Federation (SAJ) which was founded in the Tampere Workers' Hall. Haapalainen was expelled from the office in 1911 due to his drinking problem. Haapalainen now became a writer, he published and translated several books and articles focusing in trade unionism and cooperatives. Haapalainen also worked as an editor for the SAJ released monthly. In 1914, he served three months for political agitation.