Donald Trump Jr. likened his father's proposed border wall with Mexico to a zoo fence Tuesday evening, sparking a sharp backlash on social media from users who thought he was comparing immigrants to zoo animals.

“You know why you can enjoy a day at the zoo?” the son of President Donald Trump wrote in an Instagram post that has since been deleted. “Because walls work.”

Seinfeld director Larry Charles tweeted that Trump's oldest son is "so blinded by his own hubris that he can't see that once @realDonaldTrump falls, he will be nothing but a convict serving time for treason, in a cage, behind a wall."

Emily Jane Fox of Vanity Fair wrote: "Immigrants as caged animals, from the First Son."

A spokesman for Trump Jr. told the Hill that the post was highlighting the danger and violence associated with unsecured borders and that any other insinuations were distracting from "Don’s point that walls equal safety."

In 2016, Trump Jr. provoked an outcry from critics when he turned to Twitter to liken Syrian refugees to a bowl of poisoned Skittles.

The latest post came shortly after Trump declared in an Oval Office address Tuesday night that the country was facing a "crisis" on its southern border over undocumented immigrants. In his address, Trump proposed erecting steel slats to protect the border.

The younger Trump's Instagram post prompted this comment on Twitter: "Actually I can't enjoy a day at the zoo right now. The National Zoo is currently closed due to the #TrumpShutdown"

Trump Jr. has made controversial analogies on social media before, like when he compared Syrian refugees to a bowl of Skittles, in which some of the candies are poisoned.