Spanish police say that two taxi drivers protesting for tighter regulations for app-based ride-hailing services have been arrested in clashes with police in Madrid that slightly injured three officers.

The arrests came amid a second straight day of protests outside a trade exhibition center in the Spanish capital where a major tourism fair is being held. Hundreds of taxi drivers continued to block major roads in Madrid, with many wearing the yellow traffic safety vest that has become the symbol of protests in neighboring France.

Madrid taxi drivers are on a strike to demand the regional government take similar steps announced for Barcelona. Under the pressure of a week-long strike there, the Catalan regional government says it will force users of apps like Uber and Cabify to contract rides one hour in advance.

Madrid's conservative regional chief, Angel Garrido, has refused to take the same step, saying that Barcelona and Catalonia are "heading to the Middle Ages" with such a solution.

Cab drivers' unions in Barcelona also blocked major thoroughfares on Wednesday while discussing whether to accept the terms offered, while the web-based companies are threatening to cease operations in the northeastern city.

Unauto VTC, the association representing ride-hailing companies in Barcelona, says that the regulations will lead to the "disappearance" of the service and the loss of 3,500 jobs.

In a statement, it said the regional government in Catalonia "has yielded to the blackmail of the taxi drivers, who are again kidnapping the city of Barcelona and using violence to shield their monopoly."

The strike started in Barcelona on Friday, when some taxi drivers trashed cars operated by the app services Uber and Cabify. Taxi drivers in Madrid joined the protest on Monday.

On Wednesday, protesters blocked off major roads but allowed a convoy carrying King Felipe VI and Queen Letizia of Spain to enter the exhibition center where the royals opened Fitur, one of the main fairs for the global tourism industry.

Other authorities, exhibitors and guests used public transportation to reach the premises.

Previous taxi demonstrations have led to violence. A taxi driver was hospitalized on Tuesday with a serious head injury after he was ran over by a car working for an app that he tried to stop.

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Protests forced regulatory changes at the national level last year, but Spanish cab drivers consider those insufficient, arguing that their work is regulated as a public service in a way that their competitors' isn't.

This story was reported by The Associated Press.