• The Senate Judiciary Committee postponed a planned vote to authorize subpoenas for influential conservative judicial activist Leonard Leo and Republican megadonor Harlan Crow.
• The committee's Democratic majority says the subpoenas are necessary after "defensive, dismissive refusals" by Leo and Crow to fully cooperate with its Supreme Court ethics investigation.
• Crow's friendship with Justice Clarence Thomas is under scrutiny after reports indicating the justice failed to disclose luxury trips and gifts.

The Senate Judiciary Committee on Thursday postponed a planned vote to subpoena two influential conservative political figures as part of its Supreme Court ethics investigation, after Republicans on the panel filed dozens of amendments on the eve of the vote.

"We had 88 amendments filed last night, and we started going through the amendments and lining up the votes, we just didn't have time," Chairman Dick Durbin, D-Ill., told NBC News.

Minutes earlier, Durbin abruptly adjourned his committee without holding a vote to authorize subpoenas for Leonard Leo, a controversial conservative judicial activist, and Harlan Crow, a Republican megadonor whose close friendship with Supreme Court Justice Clarence Thomas has drawn intense scrutiny.

"I had the people, the problem was these amendments," Durbin said. "We ran out of time."

Durbin did not rule out the possibility of rescheduling the vote for next week, NBC reported. He said in a statement later Thursday that the committee will "continue our efforts to authorize subpoenas in the near future."

"The highest court in the land cannot have the lowest ethical standards," his statement said.

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.

"In order to inform our legislative efforts to establish an effective code of conduct," the committee "needs to understand the full scope of the court's ethical crisis," Durbin said at the start of the meeting Thursday morning.

But the committee's Republican minority quickly accused the Democrats of playing politics. Sen. Lindsey Graham, R-S.C., the panel's ranking member, said his members see the decision to "go after private individuals" as an attempt to "delegitimize" the high court, which bears a 6-3 conservative majority.

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.

Durbin responded to the report by calling for an "enforceable code of conduct" over the Supreme Court, whose nine members face little external oversight.

"This notion that they can just declare they are some royal status, and don't have to be held accountable, is impossible to justify," the chairman said ahead of Thursday's vote.

The subpoenas are part of an effort to know the "full extent of how billionaires and activists with interests before the Court use their immense wealth to buy private access to the justices," according to Durbin.

The committee previously sought testimony from Chief Justice John Roberts, who declined the invitation. In July, the panel in a party-line vote approved legislation to impose binding ethics rules on the justices.

The panel reached out to Crow demanding information, but it said it received an "inadequate" response.

The Democrats later sought information from Leo and two billionaire Republican donors, Paul Singer and Robin Arkley, after they were identified in a separate ProPublica report alleging that Justice Samuel Alito had failed to disclose a luxury Alaskan fishing trip.

Leo and Arkley refused to comply, while Singer provided a limited response, the committee said.

Last month, Durbin announced they would vote to subpoena Crow, Leo and Arkley, accusing the men of "outright defiance of legitimate oversight requests."

On Wednesday, Durbin announced that Arkley would no longer be subpoenaed, saying in a statement that he had "provided the Committee with information that he had been withholding."

That decision "underscores that the committee is not engaged in a vendetta against conservatives" and that it is "not seeking the subpoena authorization to score political points," Durbin said ahead of the vote.

Don't miss these stories from CNBC PRO:

• 75% of Warren Buffett's equity portfolio is in just 5 stocks. Here's what they are
• These two banks just hiked their 1-year CD yield to 5.3%
• A prudent way to bet on a bounce in Apple following its post-earnings decline
• Stifel says the S&P 500 will keep climbing 'wall of worry' to hit 4,400, gives 10 stocks to play rally