U.S. Senator Elizabeth Warren (D-Mass.) has claimed that crypto industry lobbying efforts “undermine” the Biden Administration’s attempts to address the role of cryptocurrency in terrorist financing.

In a letter to the Blockchain Association’s chief executive, Kristin Smith, Warren reiterated her earlier claims that cryptocurrency is used by terrorist groups including Hamas to bypass sanctions.

Warren accused the Blockchain Association and “other crypto interests” of lobbying efforts “focused on delaying and denying new rules that would restrict crypto’s use by terrorists and criminals.”

Warren added that lobbying efforts by the Blockchain Association and Coinbase’s Global Advisory Council constitute an “abuse of the revolving door” in Washington, aimed at bestowing a “veneer of legitimacy” on the crypto industry.

In her letter, Warren asked that the Blockchain Association provide details of former military, government officials and members of Congress employed by the organization, and their compensation, as well as the nature of their work and any meetings with Biden Administration officials. She also requested that the organization provide details of its code of ethics relating to the employment of former government officials.

Warren’s letter comes after the Blockchain Association sent a joint letter to members of the Senate Banking Committee and House Financial Services Committee disputing the extent to which terrorist groups such as Hamas use cryptocurrency, citing reporting by blockchain analysis firms Elliptic and Chainalysis.

In a blog post, Elliptic argued that a Wall Street Journal article reporting that Hamas and Palestinian Islamic Jihad raised “milions of dollars in crypto” and cited by Senator Warren in a letter to the Treasury had “misinterpreted” data provided by the firm.

Elliptic added that there was “no evidence to suggest that crypto fundraising has raised anything close” to the $130 million figure quoted by the WSJ and Senator Warren’s letter.

Warren’s attack on crypto lobbyists forms part of a wider effort on the Senator’s part to tackle lobbying. The Senator has proposed legislation that would crack down on stock ownership by government officials and would ban former Presidents, Vice Presidents, members of Congress, federal judges and Cabinet Secretaries from taking part in lobbying.