Jon
The CPA
If you had actually read the Emancipation Proclamation, you would see that nowhere in the document does it state that U.S. slaves were free. Rather, enemies of the United States that had slaves were free. And since the Confederacy had left the United States, guess what they were considered?
More specifically, the proclamation actually names the state in which slaves were freed, and of course they were all members of the Confederacy. Being that Lincoln was not the President of the Confederacy, he had no authority to free the slaves in those states.