Yelp is becoming a surprising weapon in the online war between liberal activists and those on the right.

Both sides are increasingly using the website to score points in a number of political and cultural controversies.

The most recent incident came after White House press secretary Sarah Huckabee Sanders was denied service at The Red Hen, a restaurant in Lexington, Va., because of the Trump administration's immigration policies.

Appalled conservatives quickly flocked to Yelp, a website that allows the public to comment and rate businesses, and overwhelmed the restaurant's page with negative reviews. Some online trolls even posted swastikas and pornography to deface the page.

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The restaurant’s rating took a serious hit, dropping from just under five stars all the way down to its current one-star rating.

Conservative personality Charlie Kirk also seized on the controversy, urging his over 600,000 Twitter followers to leave “another 100,000 [negative] reviews” on The Red Hen’s page.

Earlier this month, right-wing activists took similar action against MXDC, a Mexican restaurant in Washington, D.C.

Protesters opposing the Trump administration's policy of separating children from their families caught illegally crossing the border confronted Homeland Security Secretary Kirstjen Nielsen Kirstjen Michele NielsenMore than million in DHS contracts awarded to firm of acting secretary's wife: report DHS IG won't investigate after watchdog said Wolf, Cuccinelli appointments violated law Appeals court sides with Trump over drawdown of immigrant protections MORE, who was dining at the restaurant.

The protesters chanted slogans until Nielsen eventually left. The confrontation was caught on camera and quickly went viral.

The online anger spilled over from Yelp to similar sites, such as TripAdvisor, which froze its reviews of the restaurant. Google's own restaurant review page also appeared to temporarily block users from leaving reviews.

While other websites have experienced this problem, Yelp has been the focal point in many of the controversies. In both cases, Yelp began stepping up its monitoring of The Red Hen and MXDC's pages and actively moderating posts and reviews.

"This business is being monitored by Yelp's Support team for content related to media reports," says a banner atop both restaurant's pages.

Visitors to the pages also see a box labeled "Active Cleanup Alert."

“This business recently made waves in the news, which often means that people come to this page to post their views on the news,” it says, adding that Yelp is working “to remove both positive and negative posts that appear to be motivated more by the news coverage.”

Internet platforms being used to voice outrage or for political advocacy isn’t a new phenomenon. Political speech has long been common on Twitter and Facebook, for example, open platforms where such content is allowed.

By contrast, Yelp’s use as a tool for political advocacy is an explicit departure from its mission, to allow the public to review businesses based on personal, first-hand experiences.

“Yelp and TripAdvisor are dealing with a new phenomenon, said Cayce Myers, a communications professor at Virginia Tech University who specializes in social media.

"They’re probably going to have to figure out a new way to deal with this because it’s going to keep happening,” Myers added.

Yelp has downplayed the phenomenon and says it has the right policies in place to address it.

“We recognize that in particular instances very passionate consumers are going to express their positions on local business and they’ll take to all platforms they can find to express that opinion,” Vince Sollitto, senior vice president of corporate communications at Yelp, told The Hill.

“We’ve always taken the stance that we want to encourage people to share their experiences and then we use our systems, automated and manual, to sort through that and recommend content to our users," he continued.

“We try to err on the side of free speech and allowing people to contribute their content and express their opinions.”

Sollitto cautioned that opinions are welcome so long as they don’t violate Yelp’s user content policy.

He also pointed toward Yelp’s efforts to be transparent when a business's page was caught in a political or cultural controversy. He noted the banners that let users know page reviews were affected by news stories and that the accuracy of reviews or ratings could be temporarily affected.

Karen North, a professor at the University of Southern California’s Annenberg School for Communication and Journalism, said that while such openness can be a boost for Yelp in terms of encouraging engagement and user growth, it can also backfire.

“I don’t know the numbers on Yelp, but if they’re having engagement issues, and if this becomes a way that people can engage that isn’t provided by other platforms then it could enrich the experience of Yelp,” she said.

“But if it's too polarizing and political for an audience that’s looking for restaurant rankings then it may detract from the user experience.”

Sollitto said that he sees cases such as The Red Hen to be exceptions rather than part of a larger trend.

MXDC and The Red Hen are two of the most high-profile examples of Yelp reviews becoming overtaken in a political fight, but they are not the first. And the right isn't the only group to use Yelp to express outrage.

In 2015, an Indiana pizzeria said it would not cater for gay weddings following then-Gov. Mike Pence Michael (Mike) Richard PenceThe Hill's 12:30 Report: Ginsburg lies in repose Buttigieg stands in as Pence for Harris's debate practice Trump argues full Supreme Court needed to settle potential election disputes MORE’s (R) religious freedom law, which was criticized by some as allowing businesses to discriminate against groups on religious grounds. Its Yelp page was promptly bombarded by negative reviews.

The same year, Yelp reviewers took similar action against a dentist who hunted and killed the now-famous lion Cecil during a trip.

Trolls from the controversial imageboard 4chan have regularly engaged in similar tactics.

Some on the left have organized concerted efforts to leave negative Yelp reviews on crisis pregnancy centers. Critics claim the centers masquerade as abortion clinics when their actual function is to dissuade women from having abortions.

In a web post from 2013 that has since been taken down, NARAL Pro-Choice America made an open call for its supporters to negatively review crisis pregnancy centers on Yelp.

A Supreme Court ruling last week struck down a California state law targeting such centers. After the ruling, an online activist rallied her followers on Twitter, urging them to leave “scathing Yelp reviews” about such centers.

The number and scope of such targeted Yelp campaigns, though, from both the right and the left, seems to be intensifying.

Yelp confirmed that The Red Hen generated more negative reviews than other controversies that played out on its site.

In many cases, Yelp doesn't always catch and warn users that reviews may be influenced by political events.

Sollitto says Yelp still works to make sure only “first-person” reviews, not politically influenced ones, are tagged as recommended reviews for a business.

But he acknowledged that in politically charged times, some consumers may want to know about a business's role in political or cultural controversies.

“Some people are going to make a decision about where they will patronize based on a number of factors,” he said.

"Including the business’s beliefs and politics."