If you read the Constitution the way it was ratified, then yes, income taxes were unconstitutional. That is why the 16th was added to the Constitution. The Republicans introduced an income tax in the 1860s only to have it knocked down by the Supreme Court about 20 years later. Direct taxes were assumed to be taxes similar to a stamp act or something of that nature and even Alexander Hamilton said that a direct tax was too messy and complicated to use.
