Sen. Jeff Merkley (D-Ore.) wrote to Marco Rubio, U.S. secretary of state, with Sens. Bernie Sanders (I-Vt.), Chris Van Hollen (D-Md.) and Elizabeth Warren (D-Mass.) asking about the involvement of Liran Tancman, an unpaid adviser to the Board of Peace and reportedly a former part of the Israeli intelligence corps, in a stablecoin for Gaza.

A kind of cryptocurrency, a stablecoin’s value stays relatively constant because it is tied to a reliable asset or commodity. The stablecoin reportedly proposed by the Board of Peace would be tied to the U.S. dollar.

Gaza issues the Israeli shekel as its currency, but shekels can be hard to come by, and cash is often controlled and laundered by Hamas. A stablecoin would allow Gazans to transact digitally without the currency flowing through Hamas’s hands.

“This proposal threatens to undermine the Palestinian financial system, raises significant surveillance and ethical concerns and creates yet another opportunity for President Trump to promote stablecoin use as his own cryptocurrency company, World Liberty Financial, pushes stablecoin adoption,” the senators wrote on Thursday.

“Mr. Tancman’s failed record of privatizing traditional humanitarian functions through the Gaza Humanitarian Foundation, including findings that more than 1,200 people seeking aid were killed around GHF’s sites, underscores the risks of moving forward with poorly vetted initiatives that affect Gaza’s civilian population,” the senators wrote.

Warren signed on as ranking member of the Senate Committee on Banking, Housing and Urban Affairs.

The proposed Gaza stablecoin was reported in late February. It wasn’t clear why the senators penned the letter to Rubio on Friday.

Many reports blamed Israel initially for deaths near aid distribution sites administered by the U.S.-backed Gaza Humanitarian Foundation. A large number of such reports were debunked, or evidence showed that Hamas was responsible for the deaths.

The Palestinian terror group, which is backed by the Iranian regime, opposed the aid sites. The foundation was created, in part, to deliver aid directly to needy Palestinians without Hamas stealing the food and other supplies.

Amid a ceasefire between Israel and Hamas in January, the foundation shuttered. Agencies that have traditionally supplied aid to Gaza took over distribution.