I assume this will be challenged in court immediately. Does anyone understand whether it is likely to survive those legal challenges?

EDIT: Here is a list reported by Google search but I really do not understand or know how reasonable these challenges are.

Equal Protection: Owners may argue the tax unfairly treats similar properties differently based on second-home status, value threshold, or owner residence. This is likely a weaker challenge because tax classifications usually receive deferential rational-basis review.

Nonresident Discrimination: A challenge could claim the tax targets out-of-city, out-of-state, or foreign owners rather than property use. The law is safer if written as a tax on non-primary luxury residences, not on nonresidents as a class.

Assessment Inequality: Owners may challenge how the city values condos, co-ops, townhouses, and mixed-use properties. This could be significant if the $5 million threshold is applied inconsistently or without reliable valuation rules.

Due Process: Owners may argue the law lacks clear notice, proof, exemption, and appeal procedures. This would be especially relevant for disputes over whether a home is truly a second home.

Residency Conflicts: Taxpayers may challenge inconsistent treatment if the city treats them as NYC residents for income tax but non-primary homeowners for this tax. Clear coordination between residency rules would reduce this risk.

Home Rule Authority: Opponents may argue NYC lacks authority unless the state clearly authorizes the tax. This challenge is less likely to succeed if Albany passes valid enabling legislation and NYC follows required procedures.

Property taxes already exist. There is no obvious reason why this particular property tax would be legally problematic.

The tax is also likely politically difficult to counter. Consider how limited in scope these taxes are, how the tax revenue benefits residents who live in NYC through providing more revenue for services without taxing residents at all, and how the only constituent the taxes negatively affects are non-residents (aka it’s non-trivial to argue that these people should even be considered constituents) who benefit from the services the city offers through stable apartment prices that nicely store their wealth yet provide little value in return.

The only rebuttal one could conceive is the value these high-net-worth individuals altruistically provide the city through developing office space and giving jobs to the city is not worth risking, but that is like saying the tail wags the dog. The reason these CEOs go to NYC is because that is where the talent and economic clustering is: if these high-net-worth individuals could get the talent they need to run their firms in Miami and Austin, they would have done so already. They have tried and they have failed up until this point.

Regardless, a claim into the future in such a complex system such as the markets and the judicial system (especially a common law system) always relies on induction which is never going to be deterministic. However, this tax is just another property tax meaning it likely will stand in court. Additionally, given that the opposition has very weak rebuttals against a well-versed counterparty implies the legislature or other political machinery won’t have a strong enough incentive to fight this tax.

NYS already has tax breaks for one's primary residence which varies by income and a tax on the sale of homes >$1Mil. Given how entrenched those are, I have trouble imagining a way in which this new tax is incongruous with existing rules.