Five U.S. senators called for the designation of the Hamas-tied Turkish Charity IHH as a terrorist organization in a letter to President Obama late last month.

The letter states that last June, 87 senators urged the president to investigate IHH for possible designation under Executive Order 13244 and now, "one year later, we urge your formal designation of the IHH without delay."

The letter notes that IHH is a member of the Union of Good, an umbrella organization formed to financially support Hamas and designated by the Treasury Department in November 2008. It is signed by Senators Bill Nelson, D-Fla.; James Risch, R-Idaho, James Inhofe, R-Okla.; Mark Kirk, R-Ill. and Mike Johanns, R-Neb.

IHH's ties to Hamas have been confirmed by the U.S. government and the group is under investigation for potential designation.

IHH has partnered with Viva Palestina, a UK-based group which has delivered millions of dollars to the Hamas regime in Gaza. During Viva Palestina's third convoy that arrived in Gaza last January, Hamas Prime Minister Ismail Haniyeh told IHH members of the convoy that "The IHH has particularly delivered substantial amount of aid to the people of Gaza. IHH President Bulent Yildirim offered help and stood beside our side during the war."

IHH also helped drive last year's deadly flotilla confrontation in the Mediterranean Sea which resulted in the death of nine activists and prompted international outcry.

The group also has offices in the West Bank and the Gaza Strip. "We only work through Hamas, although we don't limit our aid to its followers," said Muhammad Kaya, who heads the IHH branch in Gaza. "We consider Israel and the United Nations to be the terrorists, not Hamas."

Read the letter here.