The company, which develops and operates private toll roads, owns nearly 31% stake in France's 2,318-km Autoroutes Paris-Rhin-Rhone (APRR) tollway, its most profitable road.

It contributed around A$557 million in earnings for its half-year ended June.

The French government on Wednesday released details on a new proposed tax regime for transport infrastructures, including motorways and airports, to raise money as it continues to invest in greener forms of energy.

"This bill includes a new tax commencing in 2024 concerning companies operating long-distance transport infrastructure," the toll road operator said in a statement.

Had the proposed tax regime been in place in 2022, two of the four motorway concessions linked to APRR would have had to pay 117 million euros in extra taxes, Atlas added.

"The adoption of this French tax has been an overhang on Atlas Arteria for several months," said Jefferies equity analysts in a note.

"There is an impact to our valuation if this tax is applied in its current draft," they added.

Shares of the company were trading down A$5.43 as of 0454 GMT and were on track for their worst day since Sept. 2022.

(Reporting by Rishav Chatterjee in Bengaluru; Editing by Sohini Goswami)

By Rishav Chatterjee