"Sen. Hyde-Smith's recent comments clearly do not reflect the values of our company and associates. As a result, we are withdrawing our support and requesting a refund of all campaign donations," Walmart said in the tweet.
Later Tuesday, when asked by CNBC about its own donation to Hyde-Smith, a spokesman for telecommunications behemoth AT&T said, "We are no longer supporting Senator Hyde-Smith and have requested a refund of our campaign contributions."
AT&T had contributed $2,000 to Hyde-Smith prior to November.
The scientific research company Leidos then told CNBC on Tuesday, "We have already requested a refund." Leidos had contributed $5,000 to Hyde-Smith.
"Remarks like those made by Senator Hyde-Smith are offensive and an affront to everything we stand for as a company. The money was sent before the remarks were public. If Leidos had been aware, we would not have made the contribution and are pursuing a refund of our contribution," the company said.
Hyde-Smith's campaign did not respond to a request for comment.
Also Tuesday, a Facebook post Hyde-Smith made in 2014 resurfaced, showing her smilingly posing wearing a Confederate cap and holding a rifle. Hyde-Smith, who took the photo while visiting the home of Confederate States of America president Jefferson Davis, wrote, "Mississippi history at its best!" in a caption accompanying the image.
In addition to AT&T, Leidos and Walmart, two other companies, Union Pacific and Boston Scientific, had already asked for their money back Monday.
All five companies acted after corporate contributions to the GOP incumbent were highlighted by the news site Popular Information, whose article about the donations was tweeted by Messing.
Federal election filings revealed that Walmart had contributed $2,000 to the campaign of Hyde-Smith.
That contribution reportedly was made Nov. 18 — around a week after the first reports that Hyde-Smith had talked about attending a hanging.
In June, Walmart had given Hyde-Smith's campaign an initial $1,000 donation.
Filings show that Blackstone's Schwarzman made his own $2,700 contribution to the senator on Nov. 14, days after exposure of her "hanging" comment. However, it is not clear if in fact that was the date the contribution was actually made, or merely reported.
On Nov. 2, Hyde-Smith, while attending a campaign stop in Tupelo, referred to a local rancher standing next to her, and said that if he "invited me to a public hanging I'd be on the front row."
That comment sparked a firestorm of criticism after it became widely known.
Mississippi has a history of lynching African-Americans and Hyde-Smith's opponent, Espy, is black.
Espy's spokesman, Danny Blanton, said, "Cindy Hyde-Smith's comments have embarrassed Mississippi, and shown why she can't be trusted to work with the businesses Mississippi needs to grow good paying jobs."
"We're confident that voters will follow Walmart's lead and dump Cindy Hyde-Smith before she has the power to do real damage to our economy," Blanton said.