Electric scooter companies Bird and Lime have scattered thousands of rentable, dockless, electric scooters across US cities over the last year. And one complaint keeps coming up: they block sidewalks.

Advocacy group Disability Rights California is now suing the two companies in federal court in San Diego for allegedly violating the Americans with Disabilities Act. The group, which is seeking class-action status for the case, says Bird and Lime are obstructing public sidewalks, making them unsafe for people with mobility and sight disabilities. Disability Rights California is also suing the City of San Diego for not maintaining accessible sidewalks.

"The scooter companies have treated our free public walkways as their own private rental offices, show rooms and storage facilities," said Bob Frank, lawyer for Neil, Dymott Attorneys, which filed the case in conjunction with Disability Rights California.  "People with disabilities need to have access to city sidewalks and their needs must come first."

Electric scooters have only been around for about a year and they've exploded in popularity. More than a dozen companies have launched the vehicles in roughly 100 US cities. But the scooters have become a controversial topic. Some people love being able to zoom around on the vehicles, while others find the scooters to be a menace.

Residents' complaints have flooded lawmakers' offices saying they've tripped on scooters or been sideswiped by riders. Many complaints say riders don't follow the laws of the road, endanger pedestrians and leave the scooters wherever they feel like it -- blocking sidewalks, parking spots, bike racks and wheelchair accesses.

Disability Rights California's lawsuit isn't the first against the scooter companies. An Austin man sued Bird earlier this month after tripping on a scooter lying in the sidewalk. And another suit was filed against Bird in October by a disabled woman in Los Angeles who also claimed the company is violating the Americans with Disabilities Act.

Disability Rights California filed its suit on behalf of four people -- all of whom are scared for their safety.

Alex Montoya, for instance, wears prosthetics on both of his arms and his right leg, which means he's a bit unsteady and slower than an average non-disabled person. Before the scooters arrived he said he liked walking in his neighborhood. But now he's afraid, according to court filings. He says he constantly has to dodge scooters, which go up to 15 mph, on sidewalks and street crossings.

Another plaintiff, Aaron Greeson, has been blind for the past 10 years. He used to walk a lot, but after several incidents when he nearly tripped on scooters or was almost hit by riders he's become scared to go out, according to court filings. Greeson said he'd only walk now if someone accompanies him.

"I never leave the Blind Center anymore," Greeson said in a statement. "I've already fallen once because of the scooters. I don't want it to happen again."

In their apps, Bird and Lime tell riders not to scoot on sidewalks and to use proper parking etiquette, but there's no real enforcement mechanism.

Bird didn't respond to request for comment on the lawsuit.

A Lime spokesman said the company doesn't comment on pending litigation but did say, "public safety has always been at the very core of everything we do at Lime. From Lime's 'Respect the Ride' campaign, which is focused on educating riders on responsible riding, to our development of built-in sensor technology to detect if a rider is abiding by local riding laws, we are committed to keeping our communities safe for everyone."

A spokeswoman for San Diego's City Attorney Mara Elliott said their office is reviewing the lawsuit and will respond through the courts.

Disability Rights California is asking the court to declare an order to stop Bird and Lime from using sidewalks, crosswalks, curb ramps, transit stops, pedestrian crossings and other walkways in San Diego. It's also asking for statutory damages and attorneys' fees.

"People with disabilities should not have to stay in their houses because they are afraid to venture out the door due to scooters blocking their pathway everywhere they go," Ann Menasche, lawyer for Disability Rights California, said in a statement. "They have a right to use the city sidewalks just like everyone else who lives or visits here."

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