The main purpose of this article is to demarcate the influence of Catholic interest groups in Poland on the attempts to introduce legislation that would regulate the legal status of civil unions. Catholic interest groups are defined as an association of individuals, organisations or institutions which articulate postulates of the Catholic Church. In order to fulfil their agendas, these groups, especially pro-life groups, apply various methods of lobbying, persuasion or moral sanction. The article includes the author’s own typology of influence of these groups on political institutions and their environment. Selected methods of influence were applied during debates in the Sejm on the draft bills concerning legalization of civil unions, including those between people of the same sex. Catholic interest groups opposed those regulations.