Environmental activists Client Earth have launched proceedings against the UK Government in the High Court.
Their case centres on obligations the Government are under to improve air pollution in the UK.
Air pollution is an environmental issue with severe consequences for health and safety. Around 40,000 people die early from air pollution, according to the organisation.
This is not the first time Client Earth have taken the Government to Court. The Supreme Court, in 2015, ordered the Government to produce effective and satisfactory plans to combat air pollution, but Client Earth say the plans offered are below what is required, and will not make a significant effect on air pollution by the deadline of 2025.
A Defra spokesman said: "Our plans clearly set out how we will improve the UK's air quality through a new programme of clean air zones, which alongside national action and continued investment in clean technologies will create cleaner, healthier air for all."
