Facebook and Twitter affixed labels to the video pointing to accurate information about voting, but neither company said the video violated its election integrity rules in a way that would result in it being removed.
Twitter labeled the video only after being asked about it by CNN on Wednesday. The video had been on its site since Monday.
"The radical left are laying the groundwork to steal this election from my father," Trump Jr. said in the video posted by the Trump campaign. He added, "Their plan is to add millions of fraudulent ballots that can cancel your vote and overturn the election."
Facts First: There is no factual basis for the claim that the left plans to use "millions of fraudulent ballots" or seeks to "steal this election" from President Donald Trump. The President himself has referred this week, also with no basis, to "fake ballots." Trump has made repeated false and misleading claims calling the integrity of the election into question.
It is not entirely clear what the President or his son mean when they talk about fake or fraudulent ballots, but Trump and his allies have baselessly claimed that "unsolicited" mail-in ballots will be rife with voter fraud.
States have numerous safeguards in place to prevent against voter fraud, which is exceedingly rare. And some states, including reliably Republican Utah, have long sent out "unsolicited" ballots to all registered voters with no major incident.
Facebook spokesperson Andy Stone said the company had affixed a label to the video of Trump Jr. and pointed to a post outlining the company's policy.
"We will attach an informational label to content that seeks to delegitimize the outcome of the election or discuss the legitimacy of voting methods, for example, by claiming that lawful methods of voting will lead to fraud," it said.
Reached for comment on Wednesday, a Twitter spokesperson said, "We have placed a label on this Tweet, in line with our recently-updated Civic Integrity Policy."