40 Democratic members of the US House of Representatives signed a letter to President Joe Biden Friday urging him to cease arms transfers to Israel in the wake of an Israeli airstrike that killed seven humanitarian aid workers in Gaza.

The letter states:

We write to express our shared concern and outrage regarding the recent Israeli airstrike which killed seven World Central Kitchen aid workers, including an American citizen. In light of this incident, we strongly urge you to reconsider your recent decision to authorize the transfer of a new arms package to Israel, and to withhold this and any future offensive arms transfers until a full investigation into the airstrike is completed. If this strike is found to have violated U.S. or international law, we urge you to continue withholding these transfers until those responsible are held accountable.

The letter also implores Biden to “conduct a thorough investigation into this airstrike to determine how the aid convoy could have been mistakenly targeted despite coordinating their movements with the Israeli military and traveling in clearly marked vehicles.” Additionally, the letter expressed concern over Biden’s recent authorization of arms to Israel, which included bombs and fighter jets.

After the airstrike, Biden called for an immediate ceasefire in Gaza. In March, before the airstrike, Biden signed an appropriations bill that continues the US’s annual security commitment of $3.3 billion to Israel through grants and banned funding to the UN Relief and Works Agency for Palestine Refugees (UNRWA).

The Friday letter comes after an Israeli airstrike killed seven humanitarian aid workers from World Central Kitchen (WCK) on Tuesday. Israel Prime Minister Benjamin Netanyahu announced that this was an “unintended strike.” In response to the attack, the IDF dismissed two officers following an internal investigation into the incident. After this investigation, WCK called for an independent investigation into the strikes. On Saturday, Australian Foreign Minister Penny Wong announced that the government would appoint a special advisor to investigate the incident and urged Israel to preserve all evidence.