"Attorney General Barr has deliberately misrepresented key aspects of Mueller’s report and decisions in the investigation, which has helped further the president’s false narrative about the investigation," he said.
He pointed to alleged disparities between Barr's summary of Special Counsel Robert Mueller's report and what Mueller actually stated.
Amash went on to argue Barr muddied why Mueller refused to indict Trump, saying that he did so not because of "legal/factual issues specific to Trump's actions."
"As a result of Barr’s March 24 letter, the public and Congress were misled," Amash said in another tweet.
Barr, meanwhile, has pursued the president's plan to further investigate the Russia probe's origins.
Amash also accused Barr of effectively lying about Mueller's discontent with Barr's letter from March.
"Barr has so far successfully used his position to sell the president’s false narrative to the American people," he said. "This will continue if those who have read the report do not start pushing back on his misrepresentations and share the truth."
The Justice Department did not immediately respond to Fox News' request for comment.
Amash has already attacked Barr in a series of other tweets, but Tuesday's thread focused more intensely on the attorney general. In another thread from May, Amash similarly accused Barr of deliberately misleading the public. He also called for President Trump's impeachment and said the president violated the public's trust.
In a statement provided to Fox News at the time, Republican National Committee Chairwoman Ronna McDaniel suggested that Amash was parroting Democratic talking points and focusing on the wrong issues.
“It’s sad to see Congressman Amash parroting the Democrats’ talking points on Russia. The only people still fixated on the Russia collusion hoax are political foes of President Trump hoping to defeat him in 2020 by any desperate means possible," she said.
RNC spokesman Steve Guest responded to Amash's Tuesday thread by accusing him of trafficking in "ridiculous smears." "It is a shame that Congressman Amash continues to traffic in ridiculous smears that only fuel the Democrats’ absurd collusion hoax," he said.
Trump himself chimed in at the time, calling Amash a "total lightweight."
:"Justin is a loser who sadly plays right into our opponents (sic) hands!" he also said.