Drug giant Pfizer on Wednesday became the sixth big company to request a refund of its campaign contribution to Sen. Cindy Hyde-Smith in light of the Mississippi Republican's controversial "joke" comments about attending a hanging and favoring voter suppression.

But ex-Facebook President Sean Parker is not asking for the return of his money backing the election of Hyde-Smith to a full term over Democratic challenger Mike Espy, even as Parker condemned her comments.

"We condemn racism and bigotry in all its forms," Pfizer told CNBC. "We are withdrawing our support and have requested a full refund of our contributions."

Pfizer had contributed a total of $5,000 to Hyde-Smith in two donations, one in June, the other in September.

Pfizer joins Walmart, AT&T, Boston Scientific, Union Pacific, and Leidos in asking for campaign contributions to be returned.

Later Wednesday, California-based biotechnology company Amgen told CNBC that it is also requesting a refund of its campaign contributions to Hyde-Smith. The company had donated at least $2,000 to Hyde-Smith's Senate campaign, according to a Nov. 1 Federal Election Commission filing.

"Amgen is committed to a culture of diversity and inclusion. We believe that an environment of diversity and inclusion fosters innovation, which drives our ability to serve patients," an Amgen spokeswoman said in an email to CNBC.

Amgen's request brought the total number of companies seeking refunds from Hyde-Smith to seven.

The corporate moves came just days after the news site Popular Information highlighted Hyde-Smith's corporate support.

Hyde-Smith faces a runoff election against Espy, a former Mississippi congressman and U.S. Agriculture secretary, who is looking to become the first black senator from the state since the Reconstruction period after the Civil War.

As a rule, a Republican such as Hyde-Smith, who was appointed in March to replace ailing Sen. Thad Cochran, would be expected to skate to election in Mississippi.

But this year, Hyde-Smith's comments — and Facebook feed — have made the race closer to a toss-up. Both have been seen by many people as echoes of Mississippi's past as a bastion of slavery and of repression of black voting rights.

Earlier this month it was revealed that she quipped to a political supporter at an event that "If he invited me to a public hanging, I'd be on the front row."

On Tuesday night, in a debate with Espy, Hyde-Smith said, "This comment was twisted, was turned into a weapon to be used against me."

She said that if anyone was offended by the remark, "I certainly apologize."

Espy told her: "No one twisted your comments."

""They came out of your mouth. I don't know what's in your heart — but we all know what came out of your mouth. ... It's caused our state harm. It's given our state another black eye that we don't need," Espy said.

Last week, another video surfaced in which Hyde-Smith was heard saying it might be "a great idea" to make it more difficult for some people to vote. She had mentioned "liberals" right before making that comment, which her spokeswoman claimed was done in jest.