Jeremy Corbyn has called for laws to stop the Government acting in Syria without the backing of MPs.
He said the introduction of a War Powers Act is needed to stop governments launching military action in most circumstances without the backing of MPs.
Mr Corbyn also said that Labour would not take any action in the country unless it had the backing of Russia.
But Russia has repeatedly used its UN veto to block sanctions and investigations during the civil war in Syria.
Theresa May will face opposition questions in the Commons on Monday, where she is expected to explain why she ordered missile attacks on Syria, as part of a joint operation with the United States and France.
When asked under what circumstances would he back strikes in Syria, Mr Corbyn told BBC One's The Andrew Marr Show: "I can only countenance involvement in Syria if there is a UN authority behind it.
"If we could get to a process in the UN where you get to a ceasefire, you get to a political solution, you then may well get to a situation where there could be a UN force established to enforce that ceasefire."
Shadow foreign secretary, Emily Thornberry, also called for new laws to stop military action being taken without a vote in Parliament.
She told ITV's Peston On Sunday that taking military action against Bashar Assad's regime had been the "wrong thing to do".
"We think that it should be in law that there should be a vote in Parliament before we take military action.
"Not urgent cases. Clearly not when we are under attack or the Prime Minister has been kidnapped, or anything like that."
No Plans For Legislation
However, David Lidington MP, the Prime Minister's deputy, said there were "no plans" for such legislation.
Mr Lidington said he was "not going to rule anything in or rule anything out" about whether the Government would allow MPs to vote if any further action is taken a vote in Syria.
Foreign Secretary, Boris Johnson MP, told Mr Marr: "There is no proposal on the table at the moment for further attacks because so far - thank heavens - the Assad regime has not been so foolish to launch another chemical weapons attack."
"If and when such a thing were to happen then clearly, with allies, we would study what the options were.”
Russia lost its bid to secure a resolution at an emergency meeting of the United Nations Security Council condemning the "aggression" in Syria.
US ambassador, Nikki Haley, told the meeting that President Donald Trump has warned that America is "locked and loaded" if there is further use of chemical weapons in Syria.
Mrs May insisted the action was "legal" and, speaking in Number 10, she defended taking military action without the backing of Parliament.
She said: "We agreed that it was both right and legal to take military action together with our closest allies."
Lord Dannatt, former head of the British Army, writing in the Mail on Sunday, said it was "wholly right" that Syria was subject to sanctions from the UK, US and France following the "appalling" use of alleged chemical weapons by the Assad regime.
The Chief of the General Staff from 2006 to 2009, wrote:
"The Prime Minister...deserves our congratulations for having the moral courage to do the right thing at the right time.
"Always seeking approval from Parliament is a recipe for inaction."