France's iconic Eiffel Tower was closed for a fourth day on Thursday as employees extended a strike over the monument's management, unions said.

The stoppage at one of the world's best-known tourist sites is the second within two months in protest of what unions say is insufficient investment.

The tower's operator, SETE, has advised ticket holders to check its website before showing up, or to postpone their visit. E-ticket holders were asked to check their e-mails for further information.

Ticket holders will be reimbursed, the operator said.

Unions have criticised SETE for basing its business model on what they say is an inflated estimate of future visitor numbers, while underestimating repair and maintenance costs.

Union representatives were to meet SETE management in the afternoon, they told AFP.

Unions have also called on the city of Paris "to be reasonable with their financial demands to ensure the survival of the monument and the company operating it".

Their main grievance is that city hall is charging the Eiffel Tower's operator a leasing fee they say is too high, sapping funds for necessary maintenance work.

The Eiffel Tower booked a shortfall of around 120 million euros ($130 million) during the Covid pandemic in 2020 and 2021.

Its operator has since received a recapitalisation of 60 million euros, which unions say is insufficient given that major maintenance work is needed, including a fresh paint job.

Visitor numbers at the Eiffel Tower dropped sharply during Covid due to closures and travel restrictions, but recovered to 5.9 million in 2022 and 6.3 million last year.