Washington (CNN)Secretary of State Rex Tillerson is moving to eliminate or downgrade special envoy positions at the State Department, including the representative for climate change, a step that is sure to ignite vociferous opposition from some members of Congress.

In a letter obtained by CNN and written to Senator Bob Corker, the Tennessee Republican who heads the foreign relations committee, Tillerson said he would end or transfer as many as three dozen special envoy positions.

"I believe that the Department will be able to better execute its mission by integrating certain envoys and special representative offices within the regional and functional bureaus," Tillerson wrote Corker, "and eliminating those that have accomplished or outlived their original purpose."

Special envoys for Syria, Sudan and South Sudan, and the Arctic will be eliminated.