American Airlines and United Airlines both told the federal government to stop using their planes to transport children who have been separated from their families at the US-Mexico border, after a Facebook post went viral claiming they were doing just that.

American said it has no way of knowing for sure whether its aircraft has been used to transport migrant children who have been separated from their families, and United said research failed to reveal any evidence separated children were being flown on their planes.

Still, stories of distressed migrant children being transported on airplanes were spreading, and the airlines chose to respond.

How the government is responding: The Department of Homeland Security criticized the airlines' requests to not partner with the agency, saying the partnership was a way to "swiftly reunite unaccompanied illegal immigrant children with their families." Tyler Houlton, press secretary for the Department of Homeland Security, also tweeted, “Despite being provided facts on this issue, these airlines clearly do not understand our immigration laws and the long-standing devastating loopholes that have caused the crisis at our southern border.”

How all of this started

The news coverage of the border crisis and family separations has included stories of wailing cries from children asking for their parents, harsh living conditions and understaffed facilities, sparking waves of outrage against the policy.

But then a Facebook post began circulating last week that claims to be the story of a flight attendant on an unnamed airline who watched 16 migrant children dressed in Walmart sweats board a flight from Arizona to Miami just after midnight.

CNN has not confirmed the veracity of the Facebook claim.