As some economists such as former U.S. Treasury Secretary Lawrence Summers warn the Fed will err if it raises interest rates in December, Paul Mortimer-Lee of BNP Paribas SA is taking a different tack as he argues it may have already blundered by not hiking sooner.

"The die may already be cast and the path to the next recession may have been taken," Mortimer-Lee, BNP Paribas's chief economist for North America, told clients in a report last week. "The reason for our recession concern is not so much because of what the Fed is about to do -- likely embark on a slow hiking cycle beginning in December -- but because it did not start the tightening much sooner."

His worry is that by waiting for the unemployment rate to fall to 5 percent, as it did in October, the Fed has delayed too long to achieve a soft-landing. That level is already around the 4.9 percent rate Fed officials reckon pushes up prices, but that estimate could be too low and a recent pickup in wages suggests joblessness could already be beneath the inflation trigger, he said.

"The lower the unemployment rate goes, the greater the chances that this will end in recession, further disinflation and a return to zero rates," said Mortimer-Lee, a former Bank of England economist.