Hillary Clinton and Bernie Sanders wave following the First in the South Presidential Candidates Forum held at Winthrop University in Rock Hill, S.C., in November. (Chris Keane/Reuters)

Democratic presidential hopeful Bernie Sanders is taking flak for a television appearance Tuesday night in which he said that progressive groups like Planned Parenthood, NARAL and the Human Rights Campaign are part of “the political establishment.”

All three groups have endorsed Sanders’s rival, Hillary Clinton, in a competitive race for the Democratic nomination.

In an interview on MSNBC, the Vermont senator responded to a question about the endorsements by citing other progressive groups that have endorsed him -- Democracy for America and MoveOn.org -- and then launching into a riff about taking on “the establishment.”

[Sanders prepares to challenge Clinton on Super Tuesday and beyond]

"What we are doing in this campaign -- and it just blows my mind every day, because I see it clearly, we're taking on not only Wall Street and the economic establishment, we're taking on the political establishment,” Sanders said.

"And so I have friends and supporters in the Human Rights Fund, in Planned Parenthood," Sanders continued. "But you know what, Hillary Clinton has been around there for a very, very long time and some of these groups are, in fact, part of the establishment."

His comments prompted a flurry of statements and comments on Twitter that continued into Wednesday morning.

"Really Senator Sanders?" Clinton tweeted, using the Twitter handles of two of the organizations in question. "How can you say that groups like @PPact and @HRC are part of the 'establishment' you're taking on? --H."

The Human Rights Campaign, the nation’s largest LGBT rights organization, and Planned Parenthood, which advocates for women’s reproductive health, also took to Twitter on Tuesday night to voice their disappointment in Sanders.

Dawn Laguens, executive vice president of the Planned Parenthood Action Fund, followed up with a fuller statement Wednesday morning, saying “it's regrettable and surprising to hear Senator Sanders describe the very groups that fight on behalf of millions of often marginalized Americans --- people who still have to fight for their most basic rights --- as representing the ‘establishment.’ ”

And Ilyse Hogue, president of NARAL Pro-Choice America, weighed in on Twitter on Wednesday, saying: “Sadly, establishment is anti-choice forces out to end legal abortion & contraception, not our friends @PPact & @HRC

Clinton is scheduled to attend a NARAL dinner in New Hampshire on Friday.