The attacks occurred after taxi drivers announced an indefinite strike protesting a regional government plan to regulate the ride-hailing services, which they argued was too lax.
Taxi drivers continued to block a major street in Barcelona on Saturday, and taxi drivers in Madrid are planning to go on strike starting Monday. Regional and municipal officials were reportedly meeting again later Saturday with representatives of the taxi drivers.
Catalan public television showed images of protesters trashing cars allegedly used by the app-hailing services. One group smashed a car's windows while the driver was still inside.
Emergency services said they treated a driver after he suffered an anxiety attack when his car was attacked by a group of men.
Alberto Alvarez, spokesman for the taxi driver association Elite Taxi, condemned the violence.
"This cannot be tolerated in any way," Alvarez said. "These men are staining the image of our group."
Five people were arrested by regional police, while another two were arrested by city police, authorities said.
The taxi drivers want the regional government to force users of services like Uber to contract rides 12 hours beforehand. The regional government is proposing a 15-minute time limit.
Regional official Damia Calvet says the 12-hour limit demanded by the taxi drivers would be struck down by a court.
"We have to make it possible for taxis and cars used by ride-hailing apps to coexist," Calvet told Catalan public radio.
Taxi drivers in Barcelona and Madrid already went on strike against the internet-driven ride-hailing platforms in July.
Spanish taxi drivers complain that ride-hailing app driver compete unfairly since they don't have the same regulations and costs.