The Government has said a report on air pollution may be delayed until after the general election.
Existing plans to meet EU-mandated air quality limits, which are currently being broken across various areas of the country, were ruled as insufficient by the courts.
The Government was ordered to publish updated clean air plans by April 24 as a result.
The Department for Environment, Food and Rural Affairs has applied to delay publication of the report until after the election in June.
A spokesman said: "We are firmly committed to improving the UK's air quality and cutting harmful emissions.
"We are seeking an extension to comply with pre-election propriety rules."
James Thornton, CEO of environmental lawyers ClientEarth said the plans are essential to safeguard the public's health:
He said: "We are urgently considering the Government's application to delay the publication of the draft Air Quality Plan which was received on Friday evening, less than one working day before the plans are due.
"These plans are essential to safeguard public health and they should be put in place without delay.
"New plans were ordered by the High Court as a result of our case last year. This is not a political issue but a public health issue.
"Whichever party is in power, the British public need to see an air quality plan which relies on good scientific evidence and which ensures that people no longer have to breathe toxic air and suffer the grave consequences to their health as a result."
Polluting cars could be forced to pay up to £24 a day to drive in central London from 2019 under plans previously unveiled by Mayor Sadiq Khan.
Theresa May has in the past indicated that she will not punish drivers of old diesel cars if the Government cracks down on the motors to protect the environment.
Drivers were encouraged to switch away from petrol under Tony Blair's government and Mrs May said that would be taken "into account" in future plans.