Senior Senate Republicans on Monday threatened to indefinitely hold up the nominations of five top Treasury Department officials if the Biden administration doesn’t blacklist the firm managing Russia’s Nord Stream 2 pipeline project.

Sen. Pat Toomey (R., Pa.) and Ted Cruz (R., Texas) said they are prepared to approve the nominations, including two national security posts that oversee sanctions and counterterror finance, if the Treasury Department blacklists Russia-owned Nord Stream 2 AG.

The Biden administration has implemented sanctions against several firms that have provided support to the project but not against Nord Stream 2 AG, saying that it would irritate relations with critical ally Germany and do little to stop the project, given that it was near completion.

Gazprom, Russia’s state-controlled gas-export monopoly and the pipeline owner, said last week that construction on the pipeline had been completed. But there are still bureaucratic hurdles that have to be overcome to get it running. Nord Stream 2 is designed to accommodate the transmission of 55 billion cubic meters of gas annually, the company said.

Republicans say they are concerned the pipeline project bolsters Europe’s reliance on Russian energy and gives Moscow leverage over Washington’s trans-Atlantic allies. By holding up the five top Treasury nominations, they hope to pressure the administration into sanctioning the managing firm and stymie the pipeline’s startup.

“The administration’s so-called ‘deal’ with Germany hands Vladimir Putin a geostrategic victory, entrenches corrupt Russian influence in Europe, and drastically weakens the security of Ukraine, Poland, and other states on the frontline of Kremlin aggression,” Mr. Toomey, the ranking member of the Banking Committee, and Mr. Cruz said in a letter to the chairmen of the Senate Banking and Foreign Relations Committees.

A Treasury spokeswoman said that while the department has experienced career staff who are experts in their fields, “The Senate should move quickly to confirm these nominees who are integral to disrupting illicit finance, combating terrorism, and administering sanctions.”