The president's "zero-tolerance" policy has generated impassioned arguments over the past few weeks, while support for ending the separation of children and parents has come from both sides of the aisle.
The group shouted, "You’re eating a Mexican dinner as you’re deporting tens of thousands of people separated from their parents," and chanted "No borders, no walls, sanctuary for all," among other slogans.
Members also shouted "Have you listened to it? Have you heard the babies crying? Do you hear them crying?" in reference to the audio tape first leaked by ProPublica on Monday purporting to be a recording of immigrant children crying and begging for their parents. Nielsen was asked similar questions at the Monday briefing and she deflected.
"I have not seen something that came out today but I've been to detention centers and again I would reference you to our standards and reference you to the care provided not just by the Department of Homeland Security, but by the Department of Health and Human Services when they get to HHS," she said Monday.
Nielsen told attendees at a sheriffs conference the same day that children were treated well at detention facilities.
"It is important to note that these minors are very well taken care of -- don't believe the press. They are very well taken care of, we know this because many of you have detention facilities of your own."
In a statement, the Metro DC Democratic Socialists of America said members of the administration "will never be allowed to eat and drink in public again."
"We will not stand by and let Secretary Nielsen dine in peace, while she is directing her employees to tear little girls away from their mothers and crying boys away from their fathers at our border," said Margaret McLaughlin, a member of the MDCDSA Steering Committee, said in the statement. "Secretary Nielsen and everyone else who has carried out these brutal and cold-blooded orders to rip apart families should never be allowed to eat and drink in public again."
The video shot by the MDCDSA had garnered over 380,000 views by midnight.
Trump appeared to send a tweet of support to Nielsen at about 9 p.m., though the heckling incident was not specifically mentioned.
DHS spokesperson Tyler Houlton released a statement on Twitter saying, "While having a work dinner tonight, the Secretary and her staff heard from a small group of protestors who share her concern with our current immigration laws that have created a crisis on our southern border."
ABC News' Sofia Grimsgard contributed to this report.