I am referring to the 2017 tax law which capped the individual federal tax deduction for state and local income and property taxes or SALT at $10,000. This deduction was previously unlimited.
So before 2017 someone who owned a mansion or other expensive property as their primary residence could deduct the entire state or local property tax or income tax owed from his or her federal income tax liability. But they can't do that today.
Some people who pay high local income and property taxes don't like the new law. Not one bit. Many of the people most impacted are well off or wealthy Democrats in politically Democratic or "blue states".
It's ironic because much of the Democratic messaging is that the well off should pay their fair share, which is in part what the SALT $10,000 deduction cap does, even though that's NOT why Trump and Republicans put it into place. I think the issue is probably the perceived unfairness that someone with a million dollar home in say Texas or Alabama is, all else equal, paying less in overall taxes than someone with the same priced home in California or New York.