Germany's top court has given the green light to the cities of Stuttgart and Duesseldorf to ban older, more polluting diesel cars from entering areas worst affected by pollution.

The ruling was made Tuesday by the Federal Administrative Court in Leipzig in response to appeals from some German states against bans imposed by local courts in Stuttgart and Duesseldorf. It was purely to determine the legality of such bans; it will be up to the cities themselves to decide the specifics of any bans.

Crucially, other cities across the country now have the precedent to establish similar bans and this could lead to the federal government introducing a national policy to prevent a patchwork of different rules cropping up, though the government has played down concerns so far. Chancellor Angela Merkel even weighed in to stress that the bans were localized and did not affect the majority of car owners, Green Car Reports notes.

The ruling could also potentially lead to groups in other countries pushing for similar bans. Paris has already placed bans on older cars.

The calls for the ban on diesels, led by environmental group DUH, were prompted after roughly 70 cities in Germany exceeded European Union limits for nitrogen oxide (NOx) emissions last year. NOx is the gas at the center of the Volkswagen Group diesel scandal that emerged in 2015.

While the bans being proposed only concern older diesel cars, uncertainty regarding the rules and concerns about a wider ban being implemented will only add to diesel's decline. Already there's talk of some automakers preparing to permanently walk away from the fuel and the VW scandal has also turned off a lot of buyers from opting for diesel in the future. Add to this the improvements being made in the cost of electrification and it's easy to see demand for diesel falling further.