The warning comes as Paris is seeking to woo UK-based financial companies planning on relocating some operations because of Brexit.

In addition to regulating financial markets, AMF is in charge of supervising asset management companies.

AMF's revenue come mainly from levies on asset management companies and proceeds from taxes on financial transactions. However, the revenue has been capped at 94 million euros over the last three years, with anything leftover sent to the state coffers.

"If the cap on revenues is maintained ... 94 million euros is no longer tenable in the future," AMF Chairman Gerard Rameix told journalists on Wednesday.France's ACPR financial sector regulator also warned in November against capping its revenues at levels that could constrain its ability to supervise banks and insurers.

Recent probes by AMF include that of Muddy Waters LLC and Casino to see whether the U.S. short-seller overstepped the mark in a report criticizing the French retailer.

It has also opened a probe into the release of a hoax statement concerning French construction group Vinci sent its shares plunging.

"(The) cap is already lower than the planned spending in our budget, so that if this cap is not substantially lifted for 2018, AMF will have to drastically cut spending and reduce regulatory activities," Rameix added.

(Reporting by Matthieu Protard; Writing by Maya Nikolaeva; Editing by Leigh Thomas and Toby Chopra)