"It's not the death penalty," singer John Legend tweeted. "It's firing him from the most important job in the country because he can't be trusted with it. Real people are actually sentenced to death. This is not that."
Legend was responding to a tweet from Haley promoting an article about her comments. "This is a decision for the American people," she tweeted.
Haley had told CBS anchor Norah O'Donnell that there was nothing in the Ukraine transcript that "warrants the death penalty for the president."
Haley spoke out as House Democrats pursued an impeachment inquiry centered on President Trump's July 25 call with Ukrainian President Volodymyr Zelensky, whom he urged to investigate former Vice President Joe Biden.
In another tweet, Legend questioned Haley's credibility by suggesting she secretly knew Trump wasn't fit for office.
"You seem like a very bright person," he said. "You obviously know he's not morally or intellectually fit for office. I wish you would admit it for the sake of the nation and your own credibility."
Legend had previously attacked Trump on Thursday, tweeting that the president was a "f-----g embarrassment."