Former prosecutors from the Manhattan U.S. Attorney's Office on Thursday endorsed the New York City Bar Association's call for investigations into the Justice Department's about-face earlier this week in the sentencing of President Donald Trump's longtime ally Roger Stone, saying the move could foreshadow further erosion of prosecutorial independence.

The intervention of senior leaders Tuesday to reduce the sentencing recommendation in Stone's criminal case has been widely condemned as undercutting career prosecutors in an effort to protect the president's friends.

Four government attorneys assigned to the case have withdrawn from the proceedings, and Senate Minority Leader Chuck Schumer, D-New York, urged the Justice Department's internal watchdog to launch a probe.

In a letter to congressional leaders and the DOJ's inspector general, the City Bar late Wednesday added its voice to the mounting calls for "immediate investigations into these unusual and troubling events."

"Recent actions by the U.S. Attorney's Office for the District of Columbia, a component of the United States Department of Justice, raise serious questions about whether the Department of Justice is making prosecutorial decisions based not on neutral principles but in order to protect President Trump's supporters and friends," the group said in its letter. "In our criminal justice system, a single standard must apply to all who are accused or convicted of violating the law—unequal treatment based on political influence is to be deplored in all cases but is especially dangerous if it emanates from the presidency."

Former Southern District of New York prosecutors, contacted on Thursday, called the latest developments at the Justice Department both "horrifying" and "mortifying," and they feared that political influence from the White House could infect other areas of the DOJ's work.

"Today it's sentencing. Tomorrow its charging," said Jaimie Nawaday, a partner with Kelley Drye & Warren and former assistant U.S. attorney in the Southern District.

"If this goes unchecked, this is only the beginning," she said.

On Tuesday, the Justice Department retracted its recommendation that Stone should serve seven to nine years in prison following his conviction on charges that he had obstructed investigations into Russian interference in the 2016 election. Prosecutors instead suggested an unspecified prison term for Stone and said in a new memo that a sentence between 37 and 46 months would be "more in line with typical sentences imposed in obstruction cases."

A Justice Department spokesperson, Kerri Kupec, said department leaders had not discussed Stone's case with Trump or anyone else at the White House.

Trump, meanwhile, on Tuesday attacked both the Stone investigation and the prosecutors prosecutors who withdrew from it, following the DOJ's sentencing reversal: "Who are the four prosecutors (Mueller people?) who cut and ran after being exposed for recommending a ridiculous 9 year prison sentence to a man that got caught up in an investigation that was illegal, the Mueller Scam, and shouldn't ever even have started," he tweeted.

In a separate tweet on Wednesday, the president tweeted his "congratulations" to Attorney General William Barr Wednesday for "taking charge of a case that was totally out of control and perhaps should not have even been brought."

Barr, in an interview with ABC News on Thursday, criticized Trump's recent tweets, and said his public comments about Justice Department cases "make it impossible for me to do my job."

"To have public statements and tweets made about the department, about people in the department, our men and women here, about cases pending in the department and about judges before whom we have cases, make it impossible for me to do my job," Barr said, "and to assure the courts and the prosecutors in the department that we're doing our work with integrity."

Kupec did not respond to a request for comment.

The City Bar's letter questioned whether Trump and Barr had been "acting in concert to protect Stone," in violation of Justice Department norms.

"Only a thorough public investigation can lay bare the true facts relating to the Stone sentencing," it said. "Nothing is more important to safeguarding the proper functioning and reputation of our criminal justice system than its commitment—and ability—to deliver justice impartially for all. Special treatment for the president's friends cannot be reconciled with the ideals that govern that system."

Roland Riopelle, a former Southern District prosecutor and founder of Sercarz & Riopelle in Manhattan, said the reversal had indicated that the DOJ had "given up its semi-autonomous" status, and worried about a "purge" of government lawyers that were not sufficiently loyal to Trump.

"It's clear now that Attorney General Barr is under the complete control of Donald Trump and will do Mr. Trump's bidding, no matter how inappropriate or morally wrong," Riopelle said.

Of particular concern were ongoing probes into the conduct of Trump's associates, including former New York Mayor Rudy Giuliani, who had been reported to be under investigation in the Southern District for potential crimes related to his dealings in Ukraine.

Nawaday said it was "very likely" that that and other investigations throughout the Justice Department could now meet a swift end, after NBC News reported on Tuesday that Barr had taken over criminal matters important to the president.

"I think there is a great risk that investigations will be quietly interfered with across the country and across offices," she said.

There was no indication on Thursday that DOJ Inspector General Michael Horowitz planned to open an investigation into the matter. But any such probe could involve interviewing any whistleblowers within the DOJ who may have raised similar concerns about Barr's conduct, said Harry Sandick, a former assistant U.S. attorney in the Southern District who now chairs the City Bar's committee on federal courts. Under federal law, the inspector general would be required to protect the identities of anyone who came forward with complaints of political influence or other misdeeds.

Wednesday's letter marked the third time the City Bar has raised concerns over the actions, or inactions, he had taken in office.

Last October, the 120-year old bar association called for Barr to recuse from any matters stemming from the Trump administration's involvement in Ukraine, which included pressuring Ukrainian President Volodymyr Zelensky to announce corruption investigations into Joe Biden, the former vice president and Trump's political rival.

In another letter, dated Jan. 8, the City Bar urged Congress to open a probe into a "pattern" of behavior that threatened "public confidence in the fair and impartial administration of justice."

Sandick said the City Bar would continue to monitor Justice Department decision-making and would flag issues, as appropriate.

"It's important for a group like the City Bar … that if we see something to say something, and that's what we're doing," he said.