A pair of Democratic senators called on the Public Company Accounting Oversight Board (PCAOB) to address so-called “sham audits” of cryptocurrency companies by registered auditors in the aftermath of the collapse of FTX.

Sens. Elizabeth Warren (Mass.) and Ron Wyden (Ore.) raised concerns with the PCAOB about the “independence and methodology” of audit firms doing work for cryptocurrency companies, urging the regulator to “ensure auditor accountability and the credibility of the auditing system.”

“When PCAOB-registered auditors perform sham audits—even for firms that may lay outside of the PCAOB’s jurisdiction—they tarnish the credibility of the PCAOB and undermine confidence in the PCAOB-registered auditors that investors and the public rely on when making investment decisions,” wrote the senators Wednesday in a letter addressed to PCAOB Chair Erica Williams.