The UN Security Council will vote Tuesday on a draft resolution that would impose sanctions on Syria for the use of chemical weapons, diplomats said.
Russia has vowed to use its veto to block the measure, which would be the seventh time that Moscow has resorted to its veto power to shield its Damascus ally.
The vote is scheduled for 11:30 am (1630 GMT).
The proposed resolution drafted by the United States, Britain and France would slap sanctions on 11 Syrian nationals and 10 entities linked to chemical attacks in the nearly six-year war.
It would also ban the sale, supply or transfer of helicopters and related materiel, including spare parts, to the Syrian armed forces or the government.
The proposals follows a UN-led investigation which concluded in October that the Syrian air force had dropped chlorine barrel-bombs from helicopters on three opposition-held villages in 2014 and 2015.
The joint panel of the United Nations and the Organization for the Prohibition of Chemical Weapons (OPCW) also found that Islamic State jihadists had used mustard gas in an attack in 2015.
Russian Deputy Ambassador Vladimir Safronkov said Friday that Moscow would veto the measure because it was "one-sided" and based on "insufficient proof."
The Syrian government has repeatedly denied using chemical weapons in the war that has killed 310,000 people since March 2011.