In an interview with Fox News, President Trump shared the highly unusual opinion that it “almost ought to be outlawed” for federal criminal defendants to cooperate with the government in exchange for more-lenient sentencing.

“If somebody defrauded a bank and he’s going to get 10 years in jail or 20 years in jail, but if you can say something bad about Donald Trump and you’ll go down to two years or three years, which is the deal [Michael Cohen] made,” he told Fox’s Ainsley Earhardt.

“I’ve had many friends involved in this stuff,” the president added. “It’s called ‘flipping,’ and it almost ought to be illegal.”

The types of arrangements Trump was referring to typically happen as part of plea bargains, which are extremely common in federal criminal cases. “Plea bargaining is a defining, if not the defining, feature of the federal criminal justice system,” as a 2011 Justice Department report characterized it, quoting earlier research.

In fiscal 2017, the last year for which complete data is available, nearly 90 percent of the 75,163 defendants in federal criminal cases ultimately opted to plead guilty rather than take the case to trial. That number has remained above the 80 percent mark for the past two decades.

Plea agreements weren’t always this common, but their use increased considerably following “a shift to tougher sentencing laws in the 1980s,” according to the Rockefeller College of Public Affairs and Policy at the University at Albany. “More defendants are accepting plea bargains rather than taking the risk of going to trial, which could result in harsher penalties.”

Not all plea agreements come with a promise from the defendant to cooperate in other criminal cases, which is the practice singled out for criticism by Trump. But many do. A 2016 report by the U.S. Sentencing Commission found that in each year between 2009 and 2014, between 9,000 and 10,000 federal defendants received a reduced sentence for providing “substantial assistance” to the government before sentencing. Each year roughly 2,000 additional offenders also received sentence adjustments for offering assistance after their initial sentencing.

Many criminal-justice reform groups have criticized the plea-bargaining and sentencing system as highly coercive and punitive. In drug cases, in particular, prosecutors have been accused of threatening defendants with extremely harsh sentences for relatively minor infractions in the hope of getting them to plead guilty.

Most critics of the system, however, have focused on its effects on poor defendants and low-level offenders, who may feel they have no other choice but to accept the government’s bargain to avoid a protracted, costly and potentially unsuccessful court battle.

Advocates for changes have tended to be less concerned about plea bargains involving crimes committed by high-level associates of U.S. presidents.