ATLANTA — Next to Fabian Williams’s fresh mural and around a corner from a wasp-infested wall where he had painted another one, the graffitied doors along Flat Shoals Avenue seemed like an ideal canvas.

“So, I did this,” Mr. Williams said last week as he stood between a weave shop and a tax preparation office and a few feet from a recently finished aerosols-and-acrylics depiction of James Baldwin, the novelist and social critic.

The owner of the tax business loved the painting, which hardly seemed out of place in a city full of colorful visual tributes to cultural figures, civil rights heroes and local music. But to some here, the Baldwin mural is like many other works of street art on private property: potentially illegal because it is in public view and displayed without a series of government approvals detailed in a seldom-enforced 2003 city ordinance.

This spring, the city abruptly suggested that it might begin to carry out the ordinance, leaving Atlanta in a dispute of art and municipal zoning that turns on constitutional principles and quickly landed in court.