The worst thing about touring immigrant detention facilities at the border was seeing cruelty occur under the American flags hung everywhere, Rep. Alexandria Ocasio-Cortez (D-N.Y.) said Friday while testifying on family separations and the treatment of migrants .

Children are being separated from their families in front of an American flag, the congresswoman told the House Oversight Committee as she fought back tears. We cannot allow for this.

Ocasio-Cortez, a fierce critic of the Trump administration, was among four Democratic members of Congress to testify before fellow lawmakers about what they saw during visits to the border. They described seeing migrants covered in filth from an inability to shower or change, with canker sores from unhealthy food, and only thin blankets for sleeping on concrete. They called on Congress to act as migrants report overcrowded facilities and little access to care or medication.

The Trump administration has blamed the number of undocumented immigrants arriving at the border which dipped last month but hit record numbers earlier this year on loose immigration laws, demanding more funding, a border wall and legal changes to restrict access to asylum.

But the Democrats argued the administration has exacerbated the crisis through its policies, including the family separations it carried out last year.