MPs are considering Parliament's role in approving military action in Syria after Theresa May authorised air strikes without consulting them.
The emergency debate was secured by Jeremy Corbyn, who accused the PM of by-passing Parliament.
Mrs May defended her decision during six hours of debate on Monday.
She said there was evidence the Assad government was behind the chemical weapons attack in Douma and it was "legally right" to join the strikes.
Labour leader Mr Corbyn said the decision to authorise air strikes without Parliament's approval set a precedent for possible, more dangerous action in the future.
He said the debate was needed to clarify the government's obligation to consult MPs before military intervention, which is the current convention.
BBC News political correspondent Alex Forsyth said Tuesday's debate was not expected to result in a binding vote, but could inflict some political damage.
Even some MPs who supported Mrs May's decision to order strikes expressed frustration that Parliament was by-passed.
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On Monday, Mr Corbyn said the government must be "accountable to this Parliament and not to the whims of this US president".
He questioned who was responsible for the attack, saying that while it was "highly likely" the Assad regime was behind it, other groups had carried out similar attacks.
But some Labour MPs backed the decision to launch air strikes.
Mrs May said it was in the UK's national interest to act - insisting that "we have not done this because President Trump asked us to but because it was the right thing to do".
Monday's debate ended with a vote, forced by the SNP, on whether the House had sufficiently debated the matter of Syria.
The government won the motion by 314 to 36 votes, a majority of 278, with Labour abstaining.
Sites near Damascus and Homs were hit on Saturday by the US, French and UK in response to the alleged chemical attack on Douma on 7 April.
It is thought President Bashar al-Assad's regime had been stockpiling materials used to make chemical weapons at those sites, the Ministry of Defence said.
Both Syria, which denies any chemical use, and Russia, which provides military support to the Syrian government, have reacted angrily to the action.
Downing Street published its legal case for its part in the strikes, stating that the action was legally justified on humanitarian grounds.
The UK and US have said the strikes were successful, with President Trump warning the US is "locked and loaded" for further action if there are more chemical attacks.
On Saturday, the UN Security Council rejected a resolution drafted by Russia, while all Nato allies have given the military action their full support.