French police have used batons and pepper spray to clear Catalan independence activists who have been blocking the motorway between France and Spain in the hope of bringing the Spanish government to the negotiating table.

Gendarmes moved in on hundreds of protesters gathered around La Jonquera crossing early on Tuesday as officers from the Catalan regional force, the Mossos d’Esquadra, ordered the demonstrators to remove their vehicles and leave the area.

The police operation led to scuffles and some protesters could be seen crying from the effects of the spray. Officers then began towing away vehicles and debris with the aim of reopening the road to traffic.

The protest, which had been due to last three days, was called by Tsunami Democràtic, the anonymous pro-independence group that co-ordinated the blockade of Barcelona-El Prat airport last month.

Protesters closed off both sides of the road at La Jonquera. Photograph: Felipe Dana/AP

The group, which says it is committed to non-violent action, began its protests in mid-October after the Spanish supreme court jailed nine Catalan separatist leaders for sedition over their role in the failed push for regional independence two years ago.

Q&A What do the lengthy Catalan sentences mean? Show Despite the long sentences handed down by the supreme court on 14 October, some of the nine leaders convicted of sedition and misuse of public funds could soon be eligible to apply for “semi-liberty”, allowing them out of prison on a regular basis.

Josep María Tamarit, a professor of criminal law at the Open University of Catalonia, said that in cases where a sentence of five years or more was handed out, a court could stipulate “that half the sentence has to be served before prisoners are eligible for semi-liberty”. However, the supreme court turned down prosecutors’ request for such an order in the Catalan case. That means that Jordi Sànchez and Jordi Cuixart – who have now served two years in pre-trial detention – could apply to be allowed out on licence as soon as they have served a quarter of their sentences, which would be in January next year. Oriol Junqueras, who received the longest sentence – 13 years – would have to wait about 15 months before applying. Those convicted can complain to Spain’s constitutional court and then put their case before the European court of human rights in Strasbourg. The Spanish government has the power to issue pardons if they are requested and if the person convicted shows repentance for their crime. However, such a move would have profound political consequences. Opponents of Spain’s acting prime minister, the socialist leader Pedro Sánchez, would accused him of bowing before the separatists were his government to even consider a pardon. Sam Jones Photograph: Pau Barrena/AFP

In a statement released later on Tuesday morning, Tsunami Democràtic urged its followers to block the border at Behobia in the Basque country from 6pm.

The group said the actions, conducted under the slogan “Spain, sit and talk”, were intended to bring about a self-determination referendum in Catalonia.

Although the north-eastern Spanish region remains evenly divided over the issue of secession, successive pro-independence Catalan government have tried to push ahead with the split, putting them on a collision course with the Spanish state.

The supreme court’s decision last month was greeted with anger by many Catalans, and violent unrest broke out in Barcelona and elsewhere.

On Tuesday, a top adviser at the EU’s highest court said the European parliament should decide whether one of those jailed for sedition – the former Catalan vice-president Oriol Junqueras – should qualify for immunity because he had been elected an MEP.

French police remove barricades blocking the motorway. Photograph: Felipe Dana/AP

In a non-binding opinion, the European court of justice’s advocate general said Junqeras’s election in May meant that Spain could not suspend his mandate.

The advocate general, Maciej Szpunar, said he considered that “the European parliament should pronounce on whether to suspend or maintain the immunity of one if its members”.

The case was referred to the European court of justice by Spain’s supreme court, which had sentenced Junqueras to 13 years for sedition and misuse of public funds, barring him from taking up his seat.

Szpunar’s opinion came as the Catalan parliament once again defied Spain’s constitutional court by approving a proposal “to express its will to exercise the right to self-determination in a concrete manner”.

The motion was passed by MPs from the three regional pro-independence parties. MPs from unionist parties – the conservative People’s party, the Catalan Socialist party and the centre-right Citizens party – protested by boycotting the vote.

Spain’s constitution, drawn up following the country’s return to democracy after the Franco dictatorship, is based on “the indissoluble unity of the Spanish nation, the common and indivisible homeland of all Spaniards”.