BARCELONA, Spain — A twisted strip of yellow plastic has become the biggest weapon for Catalonia's separatists in their struggle with those who want to protect the integrity of Spain.

On any given evening, small groups of Catalan separatists gather to tie these yellow ribbons to benches, traffic posts and trash cans — or paint their likeness on sidewalks — across Barcelona and hundreds of neighboring towns and villages.

For activist Silvia Pla and her cohorts, the ribbon is a symbol of protest at the imprisonment of nine high-profile separatist leaders while they await trial on charges that include rebellion, for their role in an illegal referendum and ineffective declaration of independence last year.

The cause of freeing the jailed leaders, many of whom were members of the previous Catalan government, has become the burning issue for secessionists after they saw their breakaway bid collapse when it received no international support.

Pla, a 56-year-old illustrator of children's books who lives in the town of Cardedeu, told The Associated Press that she puts up the ribbons "to show that we will never accept" the secessionist leaders remaining behind bars.

But the littering of town squares, bridges and streets with the yellow ribbons has given life to a counter movement drawn from the other half of Catalonia's 7.5 million residents — the ones who want to maintain centuries-old ties with the rest of Spain.

Jose Casado is the spokesman for a loosely knit network of self-proclaimed "cleaning brigades." They are volunteers who meet a few times a month to scour their neighborhoods and remove as many of the yellow ribbons as they can find on public property. They use box cutters and tree pruners to snip off the ribbons, but have a rule not to touch the pro-secession flags and banners that hang from the balconies of private homes.

"What they call claiming public space in the name of the 'political prisoners,' for us is exactly the opposite," Casado, a 38-year-old boxing instructor from the coastal town of Mataro, told the AP. "These people have hurt Catalonia and tried to carry out a coup. They are supporting people who have made families fight amongst themselves."

The cleaners do their work at night, wearing full white body suits and covering their faces with hygienic masks and protective goggles, partly to conceal their identity and partly to make a statement.

"The moment that (separatist activists) know who are you, they mark the door of your house, they throw paint on your car and spread your personal information on social media," Casado claimed.

Divided by ideology, the two sides nonetheless resemble one another; both groups have sprung up over the past year on a local level, driven by social media and mobile-phone messaging services.

They also share a deep sense of aggrievement — the separatists feel abused by the central government and courts; the unionists feel demonized by the regional Catalan authorities.

The cleaning brigades argue that they are filling a gap left by Catalan authorities who have allowed the supporters of secession to turn common space into an echo chamber for their ideas.

Like many secessionists, Catalonia's regional president, Quim Torra, always wears a yellow ribbon, in his case pinned to the lapel of a dark suit. Large yellow ribbons hang from both the seat of the Catalan government and the Barcelona town hall that face one another in the center of the region's capital, and municipal street cleaners often do not remove the ribbons from public property.

"We shouldn't be doing this work, because it is work," Casado said. "You lose hours of sleep, of time with your family. It isn't fair. It is favoring one side."

So far, ugly run-ins between adversaries have mostly produced heated debates and the exchange of verbal insults. But three people were hurt in a clash last May in the coastal town of Canet de Mar when Casado's group tried to remove a bunch of yellow crosses that pro-secession activists had planted on the beach. Both sides blamed the other for the scuffle.

Also, last month a woman filed charges with the police claiming she was hit by a man who was angry at her for removing yellow ribbons in Barcelona.

In an open letter published in the newspaper El Periodico last month, Torra called the groups that take down the ribbons "violent fascists" and said the regional Catalan police should "prevent these masked, violent and intolerant individuals from believing they can act with impunity."

Citing these statements by Torra and other evidence, Spain's state prosecutor's office has opened a probe into the alleged identification by Catalan police of people who have removed ribbons. State prosecutor Jose Maria Segarra has said that her office believes that both putting up and taking down the ribbons is protected under freedom of expression.

This simmering tension is expected to get worse in this well-off corner of Spain.

Leading politicians on the center-right have recently joined in the removal of the ribbons, accusing Spain's Socialist government of being soft on the separatists.

Torra, who before becoming a lawmaker published virulent anti-Spanish views that his critics call xenophobic, has called on secessionists to crank up their activities over coming weeks to mark the anniversary of the failed secession attempt last October, and to prepare for what will likely be massive protests when the jailed leaders are tried.

Meanwhile, Spanish Prime Minister Pedro Sanchez, who inherited the Catalan crisis from his conservative predecessor, is trying to calm tensions by meeting with Torra in October after an initial meet in July.

"We know that this fall is going to heat up," Pla said. "The trials will make people come back on the street and keep up the struggle."