A lawyer for GOP megadonor Harlan Crow told Senate Judiciary Chairman Dick Durbin that his committee did not have "the authority to investigate Mr. Crow's personal friendship with Justice Clarence Thomas," in a letter Monday night obtained by CNN.

Crow declined to answer specific questions from Durbin and other Democrats on the committee, according to the letter.

The committee "has not identified a valid legislative purpose for its investigation and is not authorized to conduct an ethics investigation of a Supreme Court Justice," reads the letter from Crow's lawyer, Michael Bopp.

Durbin issued a statement Tuesday blasting Crow's response and lack of direct answers to the senators' questions.

"Harlan Crow believes the secrecy of his lavish gifts to Justice Thomas is more important than the reputation of the highest court of law in this land," Durbin said. "He is wrong."

Crow's lawyer also alleged that "the Committee's investigation is part of a larger campaign to target and intimidate Justice Thomas and unearth what the Committee apparently believes will be embarrassing details of the Justice's personal life."

Crow's relationship with Thomas has been under the spotlight since ProPublica published a series of reports detailing luxury travel and other lavish gifts that Thomas received from Crow, as well as Crow's purchase from Thomas and his family the home still lived in by the justice's mother. The real estate transaction and the bulk of the hospitality went unreported on Thomas' annual financial disclosures, as did Crow's reported payments for the tuition of a grandnephew of Thomas'

Thomas has defended the omission of the Crow-financed travel from his reports, with a statement that said the justice was advised at the time that he was not required to report the hospitality. A source close to Thomas previously told CNN he plans to amend his disclosures to reflect the real estate transaction.

In his letter, Bopp rejected Democratic claims they're looking at new ethics rules for the Supreme Court.

"The Committee's stated purpose of crafting new ethics guidelines for the Supreme Court is inconsistent with its actions and the circumstances in which this investigation was launched, all of which suggest that the Committee is targeting Justice Thomas for special and unwarranted opprobrium," Crow's attorney wrote.

"Congress does not have the constitutional power to impose ethics rules and standards on the Supreme Court," Bopp wrote, adding that "doing so would exceed Congress's Article I authority and violate basic separation of powers principles."

Durbin said in his statement that "Mr. Crow's letter relies on a separation of powers defense when Mr. Crow does not work, and has never worked, for the Supreme Court."

Crow's legal team previously sent a similar letter to Sen. Ron Wyden, the chairman of the Senate Finance Committee who had sought information from Crow about whether the luxury travel and hospitality he extended Thomas complied with tax law.

In their outreach to the Texas billionaire earlier this month, the Judiciary Committee Democrats asked Crow to provide information about gifts and payments that exceed $415 that were given to any justice of the Supreme Court or family member, as well as an itemized list of real estate transactions and trips.

The senators' inquiries also included separate letters to the holding companies that own Crow's private jet, private yacht and his Adirondacks resort, Topridge Camp, with the Democrats "seeking to identify the full extent of Mr. Crow's and the corporations' gifts to Justice Thomas."

"The appearance of special access to the Justices -- that is not available to all Americans - is corrosive to the legitimacy of the Court because, at minimum, it creates an appearance of undue influence that undermines the public's trust in the Court's impartiality," the Democratic letters said.

Crows' refusal to answer the Senate Judiciary Committee's questions comes the same week that The Atlantic published an interview with Crow, in which Crow argued that their relationship did not cross ethical lines.