Activists and a Greens MP have threatened legal action after the Western Australia police banned at least 12 people entering a designated security area where the Land Forces weapons expo will be held in Perth from 6 October.

The police used special powers given to them by the WA government last month to ban the activists from entering the area surrounding the Perth Convention and Exhibition Centre.

Two of the activists, 18-year-old Will Shanahan and 22-year-old Matilda Lane-Rose, said in a media conference held with the Greens MP Sophie McNeill on Friday they would take legal action if police and the police minister, Reece Whitby, did not revise the ban.

“We’ve sought legal advice, and we think that we have standing to pursue a judicial review into this decision,” said Lane-Rose, who works as a staffer for McNeill.