Johnson served as chairman of the Committee on Post Office and Post Roads during the Nineteenth and Twentieth Congresses. Near the end of his term in the Senate, petitioners asked Congress to prevent the handling and delivery of mail on Sunday because it violated biblical principles about not working on the Sabbath. These petitions were referred to Johnson's committee. In response, Johnson, a practicing Baptist, drafted a report now commonly referred to as "The Sunday Mail Report". In the report, presented to Congress on January 19, 1829, Johnson argued that government was "a civil, and not a religious institution", and as such could not legislate the tenets of any particular denomination. The report was applauded as an elegant defense of the doctrine of separation of church and state. But Johnson was criticized for conflicts of interest in his defense, as he had friends who were contracted to haul mail, and who would have suffered financially from such a ban.