Fifteen anti-deportation activists are facing potentially lengthy sentences when they go on trial on Monday charged with terrorism offences for blocking the takeoff of an immigration removal flight at Stansted airport in Essex.

The defendants, from the campaign group End Deportations, said they acted to oppose a racist, secretive, dangerous and unfair practice when they walked on to the airfield at Stansted and stopped a flight due to transport 50 passengers to Nigeria last year.

The Crown Prosecution Service has charged them with endangering safety at an aerodrome, an offence created in response to the 1988 Lockerbie bombing and intended to combat terrorism.

In a letter to the Guardian, David Ramsbotham, a former chief inspector of prisons, Caroline Lucas, the co-leader of the Green party, David Lammy, the Labour MP for Tottenham, Patrisse Khan-Cullors, the co-founder of Black Lives Matter, and dozens of other signatories, have called for the charges to be dropped.

“Many critics have argued that like Trump’s ‘Muslim ban’, these deportations are unjust and racist,” the letter says.

“The Stansted action was the first time a deportation flight has been grounded in the UK by people protesting against the immigration system. People who would have been forced on to the flight were able to stay in the UK because of the action, as it gave them time to have their applications heard.”

Questions are being asked about why the activists were being prosecuted for endangering the safety of an aerodrome, a rarely used charge that only the attorney general can approve that carries a potential sentence of life in prison. A CPS spokesperson said the decision was very likely to have been taken during a routine review of the case.

Diane Abbott, the shadow home secretary, criticised the “unjustified and draconian” use of terrorism laws. “Our government has just marked the centenary of votes for women, won by civil disobedience, and yet they are attacking those fighting for justice today,” she said. “I, like many others, am deeply concerned by this misuse of terror laws and the brutality of charter flights.”

The trial is scheduled to begin on Monday morning at Chelmsford crown court. A number of groups are planning solidarity demonstrations outside court.