DES MOINES, Iowa (AP) – Three groups say a proclamation signed by Iowa Gov. Terry Branstad that encourages people to participate in a statewide Bible-reading marathon is illegal. The Des Moines Register reports two of the groups, the American Civil Liberties Union of Iowa and the Freedom From Religion Foundation, say they are considering litigation. They claim the proclamation violates the U.S. Constitution by promoting Christianity.

The Iowa Atheists and Freethinkers also opposed the governor’s action. The prayer events are organized by Christian-based groups and are planned at courthouses in all 99 counties in Iowa from June 30 until July 3. Branstad signed the proclamation in April, calling it a historic event.