Refugee and asylum seeker advocates plan to blockade Wilson Security car parks in Sydney and Melbourne today, to mark 100 days of protests by people inside the Nauru detention centre.

Activists intend to target complexes in Circular Quay and Melbourne Central from 7am, insisting Wilson Security is a major detention centre industry player, which profits from people seeking asylum.

Protest organisers from the Whistleblowers, Activists and Citizens Alliance (WACA) called on people to join the blockade efforts or boycott the car parks.

"You can join us in blockading or distributing flyers at one of their central CBD carparks, or choose a car park close to you to be part of this national day of action," WACA wrote in a Facebook event description.

"Since 2013, Wilson Security has received over 478 million dollars in taxpayers' money to run the security on both Manus Island and Nauru, whilst evading paying tax in Australia (as revealed in the recently leaked Panama Papers)," the group claimed.

"Boycott them and send a strong message to Wilson Security that it is time to withdraw from the detention centre industry," WACA spokeswoman Sam Castro said.

WACA also called on people who attended workplaces or universities with a Wilson Security contract to ask management that they cancel the contract.