In a letter to John Holmes, Thomas Jefferson described the issue behind this act as "a fire bell in the night, awakened and filled me with terror".
Much of the actual act was proposed by Senator Jesse Thomas of Illinois while it was preceded by an earlier amendment proposed by Congressman James Tallmadge that would pass in the House but not the Senate.  It would effectively extend what had been Article 6 of the Northwest Ordinance Act of 1787 and Abraham Lincoln's Peoria Speech would discuss its repeal. In a letter to John Holmes, Thomas Jefferson described the issue behind this act as "a fire bell in the night, awakened and filled me with terror". Granting statehood to Maine as a free state and declaring most portions of the Louisiana Purchase north of 36 degree 30 minutes to be free, this is, FTP, what 1820 US Compromise dealing with the growth of slavery?
Much of the actual act was proposed by Senator Jesse Thomas of Illinois while it was preceded by an earlier amendment proposed by Congressman James Tallmadge that would pass in the House but not the Senate.  
{Missouri} Compromise (accept {compromise} of {1820} before {1820} is mentioned)