This letter is to John L. Lewis, head of the United Mine Workers of America. I believe the letter they both refer to was the one grandfather wrote to Donovan Richardson, who was the publisher of the Christian Science Monitor at the time. It was published on May 22, 2015, under the title "Tombstone Series ~ Those Big Business Sons of Bitches ~ Letter to Donovan Richardson ~ November 10, 1949"
Looking at previous correspondence I believe the date on this letter, in relation to the others, should have been dated January 21, 1950 and not 1949, though we'll never know for sure.