As Nancy Pelosi faces a grueling fight with her own members to regain the speaker’s gavel in January, pro-Pelosi left-wing activist groups are warning of a "backlash" against House Democrats who oppose her.

Sixteen House Democrats on Monday circulated a letter vowing to vote against Pelosi, who served in the role between 2007 and 2011, for speaker of the House -- calling for “new leadership.”

“We are thankful to Leader Pelosi for her years of service to our Country and to our Caucus. She is a historic figure whose leadership has been instrumental to some of our party’s most important legislative achievements,” the letter from both incumbent and newly elected Democrats read. “However, we also recognize that in this recent election, Democrats ran and won on a message of change.”

16 HOUSE 'NEVER NANCY' DEMS OPPOSE PELOSI FOR SPEAKER, DEMAND 'NEW LEADERSHIP'

The letter was signed by former Pelosi challenger Rep. Tim Ryan, D-Ohio, along with other members like Rep. Seth Moulton, D-Mass., Rep. Linda Sanchez, D-Calif.; and several incoming lawmakers, like member-elect Joe Cunningham of South Carolina. Rep. Marcia Fudge, D-Ohio, is considering a leadership challenge and said she will make a decision after Thanksgiving.

Pelosi must pick up a majority of the Democratic caucus in internal leadership leadership elections, then go on to win an absolute majority of the House. If 17 Democrats vote with Republicans against Pelosi on the floor, she would not have the votes needed to become speaker.

But now, with the California Democrat’s leadership on the line, left-wing activist groups and going to bat for her -- and warning of dire consequences for those who oppose her.

Left-wing group MoveOn.org tweeted Thursday that its members “strongly support and call on all members of the Democratic causus to support @NancyPelosi for Speaker."

“Were it not for her skilled and effective leadership, the [Affordable Care Act] would not be law today. Dems must reject attempts to defeat her and move caucus to the right.”

Going a step further, a MoveOn spokesman told The Daily Beast that Democrats could face primary challenges at home if they vote against Pelosi.

“If right-wing Democrats end up helping Republicans by voting against Nancy Pelosi as speaker, they can expect to face serious backlash from the same energized and mobilized base of progressive voters that just brought Democrats a majority in the House. Which certainly could extend to primaries,” Spokesman Karthik Ganapathy told The Beast.

The outlet also reported that the Daily Kos has backed Pelosi and left the door open to primarying “Never Nancy” Democrats.

“We’ll be taking a variety of factors into consideration, including this, and if good challengers run in those seats, we’ll be keeping a close eye on the situation,” communications director Carolyn Fiddler said.

This has coincided with some left-wing members of Congress quickly lining up behind Pelosi, and taking swipes at her opponents particularly due to an alleged lack of diversity. Other Pelosi supporters have used the Twitter hashtag #FiveWhiteGuys to attack the main rebels.

"I mean if anything, I think that what it does that it creates a window where we could potentially get more conservative leadership and when you actually look at the signatories, it is not necessarily reflective of the diversity of the party," Rep.-elect Alexandria Ocasio-Cortez said on MSNBC.

"There’s very few ideological diversity, it’s not like there are progressives that are signing on, it’s not like you have a broad based coalition. I’m not totally bought into the concept."



Rep. Pramila Jayapal, who is expected to chair the House Progressive Caucus, told Politico that "no one can really doubt Pelosi's progressive chops" and that they would be turning their backs on voters if they removed her.

“That drive is not going to take us in the direction that we should go,” Jayapal told the outlet last week “It’s going to be the opposite of what the election really told us, which is a much more diverse, progressive, bold agenda.”

While congressional sources told Fox News that Pelosi is “not spiteful,” one source said that “the political repercussions for trying to block Pelosi will be more pronounced outside the Congress than inside.”

“Outside, for the past two years, voters have organized themselves with great energy and passion to take back the House. Blocking Pelosi will be viewed by many as disruptive to the progress so many worked so hard to make.”

The source suggested that the “disrupter” could then attract a “primary challenge in 2020.”

Fox News' Brooke Singman contributed to this report.