Six thousand taxis blocked roads in three Portuguese cities on Friday, the country's two main taxi associations said, in protest against the smart-phone based taxi service Uber they accuse of unfair competition by flouting rules and restrictions that regulate professional vehicles.

In Lisbon alone 4,000 taxi drivers staged a go-slow to parliament in the morning, while another two demonstrations took place in Faro and Porto, the taxi associations said.

Taxi drivers say Uber, which started business in Portugal in 2014, is operating illegally in the country, and claim the company does not follow the same rules applying to taxes, insurance and taxi driver licences.

Antral, one of Portugal's main drivers' associations, obtained in 2015 a civil court ruling preventing the firm from operating nationwide, but the ruling was filed against Uber's US-based, rather than Europe-based, incarnation.

In view of the controversy, the government has this week created a working group to address the issue. A Eurosondagem poll taken between April 25-27 showed 72.3 percent of Lisbon and Porto residents are in favour of Uber and only 9 percent are against it.

This is the second protest Portuguese drivers have staged against Uber.

Similar complaints have taken place elsewhere in Europe, the United States and India.

Uber resumed its Indian operations in January after last year being banned following a rape allegation against one of its drivers.