I switched jobs twice in IL, until I finally moved to CA to work for a different employer in Oct 2015.
I made the mistake of not reporting the IL income in my 2015 tax return and IRS caught up to me eventually in 2017 for a penalty of $6.1K for which I've already paid and re-adjusted the income. The problem now appears that CA is coming after the same unreported income from IL, which they don't have any business claiming taxes on.
I hope they're wrong to want a piece of that income and I'm able to fight them off.
Thanks for your response though, hope I was able to make it clear.
