Environmental activists Extinction Rebellion are set to challenge a London-wide protest ban at the High Court.
The Metropolitan Police imposed a blanket ban across the capital last week, making any assembly of more than two people linked to XR's Autumn Uprising action - which ended on Saturday - illegal.
The group is challenging what it says is an "unprecedented and disproportionate" ban on protests.
Lawyers for XR will argue on Thursday that the ban was unlawful because the Met went beyond its powers to prohibit "multiple assemblies, both ongoing and intended".
Those bringing the action include Green Party politicians Baroness Jenny Jones and Caroline Lucas MP, and campaigner and journalist George Monbiot - who was arrested after the ban came into force.
They argue that the order was an "unprecedented and disproportionate curtailment" of the right to free speech and free assembly which risks criminalising protest about the climate and ecological emergency in the capital.
The Met contends the ban, which is no longer in place, was lawful and was the only way of tackling the disruption caused by XR.
In 10 days of protests to call for urgent action on climate change and wildlife losses, which started on October 7, XR activists shut down areas around Parliament and the Bank of England, and targeted London City Airport and Government departments.
The Met used Section 14 of the Public Order Act initially to restrict the XR protest action to Trafalgar Square, but following "continued breaches" of the order officers moved in to clear the area.
The force said 1,832 people were arrested during the protests, and more than 150 were charged with offences.
XR's stated tactics are to cause "maximum disruption" and to overwhelm the capacity in police custody, including by refusing bail after being arrested. The case will be heard by Lord Justice Dingemans and Mr Justice Chamberlain from 10.30am.