Staff at the museum voted on Tuesday to extend the protest which has kept the museum closed to thousands of would-be visitors.
Workers decided to extend their action launched last Thursday to demand 20 more people to staff the larger, renovated venue, whose world-leading impressionist collection draws three million visitors each year, the museum said.
Twenty-five years after its creation in a century-old former railway station on the south bank of the Seine, Orsay has spruced up around half of its exhibition spaces at a cost of €20.1 million ($27.6 million).
Special attention has been paid to the impressionist gallery. The museum of 19th-century art was braced for a rush of visitors keen to see masterworks by Claude Monet, Auguste Renoir or Edgar Degas in their new setting.
Four new storeys have also been built inside the museum's Amont pavilion, a vast former machine room, creating 2,000 square metres (21,500 square feet) of new hanging space devoted to putting more of its decorative arts collection on show.
Unions argue that they need the extra staff to welcome visitors adequately in the new set-up. A new staff meeting is planned for Wednesday.
The strike -- followed by 37 of the museum's 600 staff -- has so far cost it €250,000, a statement from Orsay said.
Visitors can find the latest information at the museum website.