Adbusters, the group which helped spark the Occupy movement, has put out a call for tens of thousands of protesters to occupy Chicago during the G8 and Nato summits in May.

Seeking out those it describes as "redeemers, rebels and radicals" all over the world, the Canadian activist group is calling on protesters to bring their tents and peaceful barricades to converge on the city and build a camp on public ground. By making the call international, the group said it is hoping to pull off the "biggest multinational occupation" ever.

It encourages peaceful civil disobedience and invokes the spirit of the "Chigago Seven", a group of high-profile civil rights leaders including Abbie Hoffman, who were charged with inciting riots in 1968, when the city was host to violent clashes between police and anti-Vietnam activists during the Democratic National Convention.

Protesters flocking on the city in May will face heightened security, when heads of state, Nato generals and other military leaders will be there. They will also face unique rules in the city against erecting tents, which forced Occupy Chicago to become unique in the Occupy movement for not ever setting up a permanent occupation.

Since a wave of evictions in cities and campuses across the US last November, the Occupy movement, which protested against income inequality and corporate greed, has become less visible, aside from a few rallies or demonstrations. But campaigners insist the movement continues to grow and will rise anew in the spring in time for the May offensive.

The month-long protest will focus on demands for "a Robin Hood Tax … a ban on high frequency 'flash' trading … a binding climate change accord … a 'three strikes and you're out' law for corporate criminals … an all-out initiative for a nuclear-free Middle East" and whatever it decides on general assemblies and global internet brainstorms, according to Adbusters.

Threatening civil disobedience, it added: "And this time around we're not going to put up with the kind of police repression that happened during the Democratic National Convention protests in Chicago, 1968 … nor will we abide by any phony restrictions the city of Chicago may want to impose on our first amendment rights. We'll go there with our heads held high and assemble for a month-long people's summit … we'll march and chant and sing and shout and exercise our right to tell our elected representatives what we want … the constitution will be our guide."

A spokesman for Occupy Chicago welcomed the call, and said it would be publicising it as part of its #ChicagoSpring campaign, which would include protesting at Nato and G8.

Joshua Kaunert of Occupy Chicago said: "Occupy Chicago has a lot of work to do both prior to and after these summits: Mayor 1% has turned peaceful protest and passive resistance in Chicago into a criminal act, violating our First Amendment rights. We are still in the planning stages for all of our spring actions, but we welcome all who want to speak out against the famine and war forced on the world by the G8 and Nato to join us in the streets of Chicago."

Adbusters have said they hoped 50,000 people would converge on Chicago. However, none of the recent actions by Occupy have mustered the kind of numbers that it has managed in the past.

However, Sebastian, a spokesman for Occupy Wall Street – who was unwilling to give his surname – said the adbusters call was "inspiring" and could be the spark that lights up the movement in the Spring.

"The people base is probably growing faster than we had before, as we have spent a long time in network building and outreach work. A single march in Portland was 6,000 people and we had a union march in New York of 30,000 people. The oppression of a movement makes it stronger. They are calling not just on Occupy, but on people internationally. The appeal is huge."

He said that Occupy was already planning actions in May, an important month in the civil rights calender, such as a general strike on May 1, but the adbusters call to protest for the whole month was an "inspiration."

Sam Jewel of Occupy DC said: "Everyone I've spoken to form Occupy DC is pretty excited about it. It's going to be a pretty dramatic few weeks. It will be interesting to see that will happen and whether they will respect for dissent. The mayor of Chicago hasn't ever allowed tents at Occupy Chicago. There is the whole tradition of '68 with all the police brutality there. But we are in a different era of protests now.

"There is a global consensus that wealth is too accumulated by a small percentage, and that our country is not democratic any more."