Union workers were protesting chronic understaffing, building deterioration and recent management decisions - pressures intensified by a brazen crown jewels heist in October.
The decision came during a morning general assembly after workers had adopted the walkout unanimously on Monday.
The Paris museum was already closed on Tuesday for its regular weekly shutdown.
It remained unclear whether the strike would force a full closure on Wednesday.
Visitors holding tickets queued outside the museum in the morning as management assessed staffing levels and whether enough employees were available to safely open galleries.
Tensions have been further sharpened by fallout from the theft of crown jewels during a daylight robbery that exposed serious security lapses at the museum.
Culture ministry officials held crisis talks with unions Monday and proposed to cancel a planned cut in 2026 funding, open new recruitment for gallery guards and visitor services and increase staff compensation.
Union officials said the measures fell short.
Louvre President Laurence des Cars was scheduled to appear before the Senate's culture committee later Wednesday as lawmakers continue probing security failures at the museum.
Des Cars has acknowledged an "institutional failure" following the heist but has come under renewed scrutiny after admitting she only learned of a critical 2019 security audit after the robbery.
France's Court of Auditors and a separate administrative inquiry have since criticised delays in implementing a long-promised security overhaul.
The culture ministry announced emergency anti-intrusion measures last month and assigned Philippe Jost, who oversaw the Notre Dame restoration, to help reorganise the museum.
The move was widely seen as a sign of mounting pressure on Louvre leadership.
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