WASHINGTON (Reuters) - The U.S. Senate will begin voting on Tuesday on a resolution criticizing the Trump administration’s decision to ease sanctions on companies linked to Russian oligarch Oleg Deripaska, a measure that is unlikely to pass given the Republican majority in the chamber.

FILE PHOTO: Russian aluminium tycoon Oleg Deripaska waits before the talks of Russian President Vladimir Putin with South Korean President Moon Jae-in at the Kremlin in Moscow, Russia June 22, 2018. REUTERS/Sergei Karpukhin/File Photo

Senate Democratic Leader Chuck Schumer sent a letter to Senate Republicans and Democrats on Monday urging them to support the resolution of disapproval.

The U.S. Treasury announced on Dec. 20 that it would lift sanctions imposed in April on the core businesses of Deripaska, including aluminium giant Rusal, its parent En+ and power firm EuroSibEnergo, watering down the toughest penalties imposed on Russian entities since Moscow’s 2014 annexation of Crimea.

“This is not the moment to give up a source of leverage over the Russian government,” Schumer said in a speech on Monday. Deripaska has close ties to the Kremlin.

Deripaska has agreed to pare back his controlling stakes in the companies but Schumer said he still retains too much influence on them and also argued that easing the sanctions would boost Russia’s economy.

Schumer added that the timing of the decision was inappropriate in light of the investigation into possible ties between President Donald Trump’s 2016 presidential campaign and the Russian government. Deripaska had ties with Paul Manafort, Trump’s former campaign manager, documents have shown.

“At the time when these things are coming forward, to undo the sanctions on Rusal? Very suspect, very suspect,” Schumer said.

The prospects that the measure will pass are slim. Passage would require the approval of both the Democratic-majority House and the Senate, led by Trump’s fellow Republicans, who are unlikely to break with his policy.

Trump said on Monday he never worked for Russia, his first direct denial after a report that the FBI investigated whether he acted against U.S. interests. Trump also disputed a report that he concealed details about his meetings with Russian President Vladimir Putin.

Treasury Secretary Steven Mnuchin last week assured House lawmakers that the Trump administration would keep control over the companies. House Democratic leaders had summoned Mnuchin to explain the sanctions decision in one of their first actions since taking control of the chamber on Jan 3.