Sen. Elizabeth Warren (D-Mass.) labeled the dinner “corruption, plain and simple.”

“Amid antitrust scrutiny, Facebook is going on a charm offensive with Republican lawmakers,” Warren tweeted from her presidential campaign account. “And now, Mark Zuckerberg and one of Facebook's board members — a major Trump donor — had a secret dinner with Trump.”

Warren has called for federal regulators to break up Facebook, prompting Zuckerberg to tell Facebook employees this summer that the company would have to “go to the mat” in a legal fight with her administration.

The escalating war of words between the company and Democrats like Warren has some in the party worried that Zuckerberg is throwing his lot in with the GOP to escape serious fallout in D.C. And they saw the Trump dinner as evidence that their fears are coming true, a development that could prove ominous given Facebook’s crucial role as a platform for reaching and persuading voters.

Zuckerberg and Peter Thiel — a Facebook board member and one of Trump’s most prominent allies in the tech sector — broke bread with Trump and first lady Melania Trump during a recent D.C. swing, the company confirmed Thursday.

POLITICO reported last month that Zuckerberg had previously held a series of off-the-record dinners starting in July with conservative pundits and journalists, as well as Sen. Lindsey Graham (R-S.C.). In September, Zuckerberg quietly held several meetings and at least one dinner with lawmakers, many of them prominent Republicans, to discuss concerns about the company’s conduct.

“Every time we learn more about Zuckerberg’s behavior, it’s getting much more concerning,” Ocasio-Cortez said.

Bill Russo, deputy communications director for Joe Biden’s presidential campaign, said that in light of "nearly weekly revelations about secret White House dinners and attempts to cozy up with right wing provocateurs, it is increasingly clear their choice is to put profits above the American people."

Facebook maintains that such meetings are standard practice.

“As is normal for a CEO of a major U.S. company, Mark accepted an invitation to have dinner with the President and First Lady at the White House,” a Facebook spokesperson said.

Rep. Dan Crenshaw (R-Texas) told POLITICO he doesn't understand any reason for the fuss.

“So what? That’s my reaction," Crenshaw said when asked about the secrecy and what Zuckerberg and Trump may have discussed. "Why can’t the president have a closed-door meeting?”

Graham said Thursday that his own Zuckerberg dinner had been valuable. "I enjoyed the dinner, I learned a lot and I hope the president did too," the senator told reporters.

Zuckerberg in September also huddled privately with Democratic lawmakers, including prominent congressional critics Sen. Richard Blumenthal (Conn.) and Rep. David Cicilline (R.I.).

The latest news comes as Facebook — already under the shadow of federal and state probes into whether the company's acquisitions or business practices have harmed competitors — remains caught between conflicting critiques from both sides of the aisle. Republicans accuse the company, without clear evidence, of stifling conservative viewpoints. Democrats argue that Facebook is failing to curb hate speech and misinformation, and even encouraging them with its policy against fact-checking political ads.

The Democrats’ complaints multiplied after Facebook ran an ad from Trump’s campaign that baselessly accused Biden of being involved in corruption in Ukraine. The ad has triggered vocal criticism from Biden, who otherwise tends to echo the Obama administration's friendly relations with Silicon Valley.

Trump has been the biggest-spending presidential contender by far on Facebook ads, putting in more than $16 million on the platform so far, according to POLITICO’s tracker. The anti-Biden ad also appeared on other digital platforms and several television networks, although CNN declined to air them.

Zuckerberg has defended its policy on campaign ads as reflecting its commitment to free expression.

The company has since contemplated tweaks to the policy, including limits on candidates’ ability to narrowly target would-be voters, but has so far stood by its permissive approach, even as Twitter has banned all political ads and Google on Wednesday announced some limits of its own.