Are you even allowed to introduce ex post facto taxes like this? I'm no legal expert but it seems to me that a tax is a penalty for an action and it's a violation of the 9th amendment to introduce penalties for actions that have already happened.
Ex post facto and taxes would only intersect if the due date for a tax were set prior to the date the tax was enacted into law.
But the tax is on income collected prior to the date the tax was enacted into law, so if you have collected income you already have no way to avoid paying the tax.
To my eyes, it's similar to if you were to say that everyone who wore red socks this year is going to prison, but the roundups won't start until 2021. It's already too late for me to escape the punishment for wearing red socks, which had no consequences at the time.
