The U.S. Agriculture Department must take immediate action to secure the benefits cards from which low-income families are being robbed of grocery funds, six Democratic senators urged in a letter.

Data since last fiscal year shows that the federal government has reinstated more than $150 million in stolen benefits to participants of the Supplemental Nutrition Assistance Program, or SNAP.

But the actual amount taken from needy households is most likely much higher than that, the senators wrote in a letter to Agriculture Secretary Tom Vilsack, adding that a proposed rule that the Agriculture Department has yet to release about modernizing the cards would prevent the thefts from proliferating.

“The USDA should act with urgency to require state-issued benefit cards to be protected by industry-standard payment security defenses,” read the letter, which was sent Monday evening and first shared with NBC News. It was signed by Sens. Ron Wyden, D-Ore., John Fetterman, D-Pa., Amy Klobuchar, D-Minn., Peter Welch, D-Vt., Kirsten Gillibrand, D-N.Y., and Elizabeth Warren, D-Mass.