France's Eiffel Tower was to remain closed on Saturday morning as staff voted to extend a strike over the monument's management, unions said Friday.

The stoppage since Monday 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 tourists to check its website before showing up, or to postpone their visit.

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.

The unions also say that city hall is charging the Eiffel Tower's operator a leasing fee that is too high, sapping funds for necessary maintenance work.

On Thursday, SETE promised new measures to address these concerns, including hiking the price of tickets by 20 percent.

A ticket now costs 29.40 euros ($31) for an adult to take the lift to the summit, while those who climb up partway by stairs pay a little less.

The operator also said the budget for maintenance works would be more than doubled.

But unions said the proposals were not enough.

They were to hold another meeting on Saturday morning to decide whether to prolong their protest.

SETE also pledged to sign a deal on the "employment conditions and salaries" of staff within a fortnight.

But CGT union representative Stephane Dieu said strikers rejected the offer as not what they had asked for.

Culture Minister Rachida Dati on Thursday also suggested the Eiffel Tower be classified a "historical monument" to allow the state to help fund works if needed.

"The Eiffel Tower does not have enough protection," she posted on X.

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.

The masterpiece by architect Gustave Eiffel has been repainted 19 times since it was built for the 1889 World Fair.