TUNIS - Tunisian police arrested a labour union official over a strike at a highway toll booth, union officials said on Wednesday, indicating a more direct confrontation between President Kais Saied and one of the country's strongest political forces.

The police detained Anis Kaabi, general secretary of the highways branch of the UGTT union, at his home late on Tuesday, the union's Achaab newspaper reported, saying the strike was legal.

The arrest could aggravate growing tensions between Saied and the union, which has taken an increasingly strong stance against his expansion of powers, introduction of a new political system and proposals for economic reforms.

Last month, senior UGTT official Sami Tahri said, "we can scent the authorities targeting the labour union", after its leader gave a speech criticising Saied and demanding he change tack.

The UGTT, which has more than a million members and has proven its ability to shut the economy with strikes, has played a key role in Tunisian politics since the 2011 revolution, helping broker a deal for a new constitution in 2014.

It has used increasingly strong language against Saied, while so far stopping short of any major campaign of strikes and protests to directly challenge his political agenda.

Saied, who shut down parliament in 2021, seizing most powers and moving to rule by decree before writing a new constitution, has ignored repeated UGTT demands for a national dialogue to resolve Tunisia's internal political disputes.

Highway toll booth workers went on strike this week to demand higher wages.

Hamza al-Mahmoudi, a union official, said Kaabi was arrested after a complaint from a government ministry that he was costing the state financial losses.

A spokesperson for the Interior Ministry was not immediately available for comment.

The arrest came hours after President Saied visited a National Guard barracks and told forces there in a speech that they should take action against "those who conspire against national security or against public companies".

"Those who block the road and threaten to block the motorway cannot remain outside the circle of accountability and punishment," he said.

(Reporting by Tarek Amara; Writing by Angus McDowall; Editing by Arun Koyyur)