The Mayor of London’s plans to expand a contentious charge on drivers of older, more polluting cars to the capital’s outer boroughs was ruled lawful by a judge.

Sadiq Khan was “within his powers” to order the expansion of the zone, that charges motorists to drive within it, Judge Jonathan Swift.

A group of Conservative-led local authorities sued arguing that the plans to grow the Ultra Low Emission Zone had moved too fast to enact and didn’t consult communities properly as well as it having a damaging impact on the local economy.

Critics of the expansion argue it’s unfair during a cost of living crisis to impose extra charges on motorists who need their vehicles to work. The Conservatives weaponized the issue to unexpectedly keep control of former Prime Minister Boris Johnson’s old parliamentary seat in a special election earlier this month by turning the vote into a de facto referendum on Khan’s plans.

Read More: Why London’s ULEZ Charge Became a Political Football: QuickTake

That result in turn has led Labour Leader Keir Starmer to ask Khan to “reflect” on his plans and see if there is a way to soften the impact on drivers. The Tories, meanwhile, have seized on it as a signal that they should roll back other environmental proposals in order to boost their electoral prospects.

Khan’s office has argued the decision is as much a public health policy as environmental, saying around 4,000 Londoners a year die prematurely from air pollution.

At present, the area covers a large part of London from north to south, charges £12.50 ($16) on vehicles which do not meet low emissions standards. Under Transport for London proposals, this will be expanded to include all London boroughs, covering the majority of the land inside the circular M25 motorway, from Aug. 29.

--With assistance from Alex Morales.