Trump Tower, like other skyscrapers in New York City, has a massive carbon footprint. But under a new bill expected to pass today, it will have to start cutting emissions in line with the Paris climate agreement.

The bill is part of a package called the Climate Mobilization Act, thought to be the largest single act to cut climate pollution of any city. Buildings–the largest source of emissions in the city–are at the heart of the policy changes. Large buildings will have to cut emissions 40% by 2030, and 80% by 2050. “It’s a monumental achievement,” says Pete Sikora, climate and inequality campaigns director for New York Communities for Change, one of the grassroots groups that has been campaigning for this type of law for several years.

“New York City is a very large source of climate pollution worldwide,” Sikora says. “The city also has an inequality crisis. So we wanted to attack the issue in a kind of Green New Deal style, where we’re tackling the climate crisis and fighting inequality at the same time by creating thousands of good jobs.”

Buildings larger than 25,000 square feet–from six-story walkups to One World Trade Center–make up only about 2% of the city’s real estate, but are responsible for half of total building emissions. Under the bill, which the mayor is expected to sign into law, those buildings will have to find ways to improve energy efficiency if they go above a limit on carbon pollution per square foot. Buildings with rent control have a different standard that requires low-cost energy efficiency improvements but doesn’t set a pollution limit, because major capital improvements trigger rent hikes and the city wanted to avoid that. A new Office of Building Energy Performance will run the program.

Unlike some building code requirements, building owners have flexibility in deciding which improvements to make. Some buildings that are already relatively efficient might only make small changes. Others might decide to replace windows and facades, replace outdated mechanical equipment, or add sensors that can make a building smarter. Another bill in the package enables a type of financing to pay for the changes through property assessments tied to their property tax bills, so that they don’t have to spend a large amount up front. The retrofits will create new jobs, from energy analysis of buildings to architecture, engineering, and construction work, including union, career-track jobs that employ people from communities of color, Sikora says.

Some parts of the city’s carbon footprint are outside of its direct control. Most of its electricity comes from other parts of the state. But shrinking the amount of energy that buildings use will also shrink the pollution from that electricity. Another bill in the package calls for a new study of what it would take to shut down all of the 24 fossil fuel power plants that do exist inside the city limits and replacing them with renewable power and energy storage. Yet another bill makes it easier to install wind turbines in the city. Another bill requires green roofs, with either plantings or renewable energy, on some larger buildings; another bill calls for a study of creating similar requirements on smaller buildings.

New York is the first city to set this type of emission limit on large buildings, although Washington, D.C., is also rolling out new standards on energy use (in D.C.’s case, certain buildings have to be at least as efficient as the median building of their type). But other cities are likely to follow, says Anica Landreneau, director of sustainable design at HOK, the design, architecture, engineering, and planning firm. “It makes a lot of sense because in most of these cities, buildings are 50% to 70% of carbon emissions,” she says. “And so if you want to hit these zero-carbon targets that cities are committing to, you have to do that through building stock . . . It’s really a great example of New York leadership, and I think we will see a lot of other cities follow in their footsteps.”