The 16th Amendment made an income tax constitutional when it was ratified.

Amendment XVI - Income taxes authorized. Ratified 2/3/1913.

The Congress shall have power to lay and collect taxes on incomes, from whatever source derived, without apportionment among the several States, and without regard to any census or enumeration.

It's reasonable to ask how such an amendment could win a 2/3rds majority of both houses of Congress and be ratified by the states. Easy - it was sold as a "tax on the rich." Ordinary people were told the income tax would never apply to them, so they had no opposition to it.

As for the "commerse clause", the Supreme Court bent that beyond all recognition for decades starting around the 1930s. According to a recent column, back in the 1940s a man was cited for growing food in his own yard in opposition to a law and the law was upheld. The "reasoning" was that if the man hadn't grown his own food, he would've had to buy food that might've come from other states, hence it was "interstate commerse."