"The bond market is listening. The influence of the Fed has greatly increased and the market, it is getting kind of old school where the market listens to what the Fed says," Gundlach said on CNBC's "Halftime Report."
The Federal Open Market Committee is scheduled to release its meeting statement at 2 p.m., ET. Fed Chair Janet Yellen is scheduled to hold a news conference at 2:30 p.m. Traders widely expect the central bank to raise interest rates.
"What's really important isn't the interest rate increase that we all know is going to happen," he said. "It is what happens with the Fed's rhetoric."
Last week, Gundlach said he expects the Fed to begin a campaign this month of "old-school" sequential interest rate hikes until "something breaks," such as a U.S. recession.