NEPA (the National Environmental Policy Act) is the federal law that requires environmental review for any action the federal government funds, permits, or licenses. Because the FCC licenses the spectrum that wireless towers transmit on, tower builds can trigger a NEPA review pathway before construction starts, depending on the site and scope.
In practice, most macro and small-cell sites qualify for a categorical exclusion (the lightest pathway), but every site has to be screened against floodplains, wetlands, endangered species, historic properties, and Tribal interest before it clears.