Justice Potter Stewart, who wrote the majority opinion in the Hayes case. AP Photo/John Duricka Human Rights Watch (HRW) recently revealed that many federal drug defendants are bullied into pleading guilty, and it turns out the Supreme Court has specifically said it is acceptable for prosecutors to threaten defendants in order to avoid a trial.

After HRW released its report, I spoke to Georgia State University criminal law professor Russell Covey about the negative implications of plea bargaining which he said provides a "huge incentive" for even innocent defendants to plead guilty.

One problem with plea agreements is that prosecutors often threaten to tack on additional charges if people don't plead guilty. In 1978 the Supreme Court specifically ruled that prosecutors could make such threats, Covey pointed out.

That case involved a Kentucky man named Paul Lewis Hayes who was indicted for "uttering a forged instrument in the amount of $88.30" which carried a two- to 10-year prison sentence.

The prosecutor offered to recommend a five-year sentence if he agreed to plead guilty. But the prosecutor threatened to charge Hayes under the Kentucky Habitual Criminal Act (a "three strikes and you're out" law) if Hayes didn't "save the court the inconvenience and necessity of a trial," according to court documents. Hayes — who had two other felony convictions — didn't take the deal. He got life in prison.

The case went all the way up to the U.S. Supreme Court, which ruled that the prosecutor hadn't violated Hayes' Constitutional rights.

"The thing that's really outrageous about that case is that it went to the Supreme Court and the Supreme Court affirmed the sentence as not violating any Constitutional right of the defendant," Covey told me.

Here's what Justice Potter Stewart said in the majority opinion:

The Due Process Clause of the Fourteenth Amendment is not violated when a state prosecutor carries out a threat made during plea negotiations to have the accused reindicted on more serious charges on which he is plainly subject to prosecution if he does not plead guilty to the offense with which he was originally charged.

This Court has accepted as constitutionally legitimate the simple reality that the prosecutor's interest at the bargaining table is to persuade the defendant to forgo his right to plead not guilty, and in pursuing that course here the prosecutor did not exceed constitutional bounds

By siding with the prosecution, the Supreme Court missed a huge chance to make the criminal justice system more fair, the late Harvard Law professor William Stuntz wrote in 2005. The Supreme Court could have ruled that prosecutors can't threaten charges that they don't ever apply in reality, Stuntz wrote.

"That holding would have spared Paul Hayes a life sentence for petty theft plus two prior felony convictions," Stuntz wrote in a Harvard Public Law Working Paper. "It would have spared many thousands of defendants guilty pleas produced by what amounts to legalized extortion. It probably would have spared some innocent defendants criminal convictions."