Brussels and Prague are the latest cities facing legal challenges to tackle the pollution crisis.
ClientEarth has launched legal action against the two cities for allegedly breaching EU air pollution laws.
The cases aim to oblige governments to take robust measures “to bring pollution within legal limits as soon as possible”.
The Brussels case is against the regional government and focuses on Nitrogen Dioxide (NO2), which mainly comes from diesel vehicles and calls on authorities to produce an “effective plan” to clean up the city’s air.
The environmental lawyers claim the current plan in place to improve air quality in Prague is “inadequate” and should be replaced with another that includes “concrete actions”.
ClientEarth is also taking legal action against the UK, Germany, Belgium and Poland over poor air quality.
CEO James Thornton said: “This case is part of a wave of clean air cases across Europe. In the past two weeks, Brno, Brussels and now Prague have joined the list of cities where people are fighting for their right to breathe clean air.
“Governments across the EU have been far too slow in responding to the public health crisis caused by air pollution. Toxic air contributes to more than 400,000 premature deaths in the EU every year.”
The World Bank estimates 5.5 million lives were lost worldwide in 2013 as a result of the impacts of air pollution.