New York City’s new pied-à-terre tax on luxury second homes has run into legal challenges and administrative confusion as officials try to identify which properties are not a person’s primary residence. The measure, an early tax win for Mayor Zohran Mamdani, would add a surcharge to one-, two- and three-family homes valued above $5 million and to condos and co-ops worth at least $1 million when those homes are used as non-primary residences. City officials say the tax could generate $500 million annually from wealthy owners who enjoy the city but do not pay city income taxes there. The rollout has proved difficult because ownership structures such as trusts and LLCs (limited liability companies) can obscure who really controls a property, while informal family use and rental arrangements can make residency hard to document. A group of homeowners sued, arguing the city improperly placed the burden on owners to determine whether they owe the tax. A judge temporarily paused the process this week, but the city appealed, allowing the effort to continue while the case proceeds. The tax has also triggered political blowback. President Donald Trump, whose Manhattan penthouse could be affected because his primary residence is in Florida, said he was exploring whether federal intervention could "avert this disaster, before it is too late." Mamdani has publicly championed the measure, including a video outside a penthouse bought for around $239 million by hedge fund CEO Ken Griffin. The city also published a legally required list of potentially affected owners, prompting complaints that it amounted to doxing or public shaming. About 17,000 properties later received notices inviting them to seek exemptions, and the exemption deadline was extended after complaints over erroneous letters and process difficulties. Real estate law professor Stewart Sterk said the latest case is unlikely to be the last, predicting prolonged litigation over denied exemptions and disputed residency status.