Democratic Senator Dick Durbin, the panel's chairman, said the hearing follows "a steady stream of revelations regarding justices falling short of the ethical standards expected of other federal judges" and "a crisis of public confidence" in the top U.S. judicial body.
The court did not immediately respond to a request for comment from Roberts. The chief justice is a member of the court's 6-3 conservative majority.
In inviting Roberts to testify, Durbin also said the chief justice could designate another justice to appear instead.
Thomas, the longest-serving of the court's nine justices, has been under pressure after published reports by news outlet ProPublica detailing his relationship with Harlan Crow, including real estate purchases and luxury travel paid for by the Dallas businessman.
ProPublica reported that Thomas did not publicly disclose the 2014 purchase by one of Crow's companies of properties in the Georgia city of Savannah from Thomas and his relatives, calling it the first known instance of money going directly from Crow to the justice.
ProPublica also reported that Thomas has for decades accepted luxury trips from Crow, who he considers a close friend, also without publicly disclosing them.
Durbin and other committee Democrats on April 10 had urged Roberts to investigate the Thomas situation and said that if the court does not resolve this issue on its own the panel would consider legislation to address it,
(Reporting by Susan Heavey and Jasper Ward; Editing by Scott Malone)
