According to famous stock-watcher and Wharton School professor Jeremy Siegel, very.

With inflation running at a 40-year high in the U.S., every American is starting to feel the sting of expensive gas and groceries. And the Federal Reserve is coming under mounting pressure to get even more aggressive in how much it is prepared to raise interest rates to slow down the economy.

Fed officials will announce later today how large the next interest rate hike will be, with many investors already pricing in a 75 basis points raise, higher than the 50 basis points hike Fed Chair Jerome Powell has already suggested. But Siegel is recommending that the Fed go even higher.

“I would like to see the Fed say ‘listen, we can go 100 basis points, we’re going to really be serious about this inflation,” Siegel said in an interview with CNBC Squawk Box on Wednesday.

Siegel said that the Fed had acted “too late” in confronting inflation, and that the central bank’s indecision last year means “they’ve got to go forcefully right now” with raising rates.

Siegel said that the Fed could justify such a large hike by moving forward the expected 50 point rise it had planned for July, and combining that with June’s hike.

He also added that, while a 100 basis points hike would inevitably come as an immediate shock to markets, doing so will be worth it in the long run, as such an aggressive hike would assure investors that the Fed is laser-focused on the inflation problem and is doing everything in its power to get it under control.

“The Fed needs to grab the narrative of inflation,” Siegel said. “I actually think after an initial selldown, the market would rally and say ‘you know what, the central bank is protecting our currency,’ which is something that we need.”

Earlier in June, Siegel told CNBC that inflation was “already in the pipeline,” and that “very little can be done today, except to make sure it doesn’t’ extend into 2023, ‘24, ‘25.”

Markets have been in a tailspin this week, with the S&P 500 officially entering bear market territory and both other stock indices markedly down as well. Last week, Siegel said that the market’s downturn was because investors were already pricing in fears that a recession in 2023 is imminent.

Other stock-watchers and Wall Street titans have mused about the possibility of a 100 basis points increase, although have so far given it low odds. In a note shared with clients on Monday, chief U.S. economist at JPMorgan Chase Michael Feroli wrote that there was a “non-trivial risk” of the Fed raising rates by 100 basis points, although reaffirmed that bank’s expectations that a 75 points hike was on the cards.

A 100 point rise might be an attractive option for the Federal Reserve if the central bank wants to “erase any perception that they are behind the curve,” Steven Englander, global head of G10 FX Research at Standard Chartered Bank, told Bloomberg this week. 

Doing so would amount to a “Volcker moment,” Englander said, referring to former Fed Chair Paul Volcker who raised rates as high as 20% in the 1980s to combat inflation. However, Englander put the chances of a 100 basis point hike this month at only 10%.