King Charles III risks facing rubbish-strewn streets, transport strikes and disruption to his visit when he travels to France next week for his first foreign trip.

In a sign that his schedule is still up in the air, an aide to French President Emmanuel Macron told AFP on condition of anonymity Wednesday that "the programme is still being worked out by both sides".

The British sovereign's planned tour, intended as a statement of cross-Channel friendship after years of arguments between London and Paris, comes with France in the grip of mass protests over pension reform.

Thousands of tonnes of rubbish have piled up in the streets of Paris, where Charles is due to arrive on Sunday with Queen Consort Camilla, while trade unionists have warned they might target a planned stop in Bordeaux.

Charles and Camilla were set to travel to the wine-producing city on the second leg of their visit on Tuesday, with a trip on its tramway reportedly on the agenda, as well as a visit to city hall where clashes took place at the weekend.

"Its almost certain that the king won't be able to take the tramway," Pascal Mesgueni, a local leader of the CFTC union in Bordeaux, told the Sud Ouest newspaper this week.

City transport operator Keolis has said there "will possibly be disruptions linked to the protests against pension reform."

Trade unions have called a nation-wide strike this Thursday, but their plans for next week remain unknown.

A source in the railways section of the hardline CGT union said "there will be actions around the (royal) visit" amid speculation that the eco-minded monarch might have be planning to take the train from Paris to Bordeaux.

Arrangements for French journalists wanting to cover the trip are also unclear -- rare for a trip of such diplomatic and public interest -- with media organisations still waiting to hear about accreditation procedures.

- Tricky optics -
 

The visit comes at a highly awkward moment for Macron, 45, who is set to host Charles III at a state banquet at the Versailles Palace outside the capital.

The royal location is seared into French minds as the seat of late king Louis XVI, who was hauled off to Paris during the French revolution of 1789 and executed with a guillotine four years later.

Macron is often accused by his opponents of being authoritarian and effigies of him have been repeatedly beheaded in public during protests in the past.

His decision to ram the pension legislation through parliament last week without a vote has dismayed even some of his allies.

Left-wing MP Sandrine Rousseau, a senior member of the Greens party, criticised the idea of the spectre of Macron -- "the monarch of the republic" -- welcoming the British King "when people are in the streets."

"He (Macron) should cancel this visit," she told the BFM news channel on Wednesday. "Is it really the priority to welcome Charles III in Versailles? Of course not.

"Something is happening in French society.. the priority should be speaking to society which is rising up," she added.

Macron argues that raising the retirement age by two years to 64 is needed to save money and prepare the country for its ageing population.

- Agenda -
 

After France, Charles and his wife are expected to travel to Germany.

The choice of the two European nations and close allies was widely seen as an attempt to build bridges between Britain and its biggest European partners after years of strains linked to Brexit.

According to the agenda given by Buckingham Palace, Charles was due to join Macron for a ceremony of remembrance and wreath laying at the Arc de Triomphe in Paris on Monday and also address lawmakers at the French Senate.

While in the Bordeaux region, he was also set to pay a visit to an organic vineyard, as well as tour an area devastated by wildfires last summer during an extreme drought that affected much of western Europe.