The Senate Judiciary Committee is expected to vote Thursday to approve subpoenas for two influential conservative political figures: judicial activist Leonard Leo and Harlan Crow, a Republican megadonor whose close friendship with Supreme Court Justice Clarence Thomas has drawn intense scrutiny.

The panel’s Democratic majority says the subpoenas are necessary in response to Leo’s and Crow’s “defensive, dismissive refusals” to fully cooperate with its ethics investigation into the Supreme Court.

The Senate probe stems from a bombshell ProPublica report in April that found Thomas, the most senior justice on the high court, had accepted luxury trips and other gifts from Crow for years without revealing them on his financial disclosures.

Thomas has said he had been advised that he did not have to disclose those items. He and Crow have defended their relationship and maintained that it has not affected Thomas’ business before the court.

Senate Judiciary Chairman Dick Durbin, D-Ill., promptly called for an “enforceable code of conduct” over the Supreme Court, whose nine members face little external oversight.