Eighty-one Conservative MPs have signed a letter to David Cameron demanding a House of Commons vote before the UK sends any arms to Syrian rebels.
The UK and France last week negotiated a relaxation of the EU's embargo on exporting arms to the country.
The letter, delivered to Downing Street, expressed "very real concern" over the UK being pulled into the conflict in Syria.
The government said any move to arm rebels would be subject to a vote.
Tens of thousands of people have died in fighting between the rebels and forces loyal to President Bashar al-Assad, which began in early 2011.
Addressing the Commons on Monday, the prime minister said no decision hade been reached on whether the UK would send arms to the rebels.
But Russia has insisted it is going ahead with the sale of a surface-to-air missile defence system to President Assad's regime.
The letter to Mr Cameron, written by Andrew Bridgen, MP for North West Leicestershire, said there was "very real concern amongst colleagues and the public about the possibility of British involvement in Syria escalating".
It asked for "assurances that prior to any decision being taken to supply arms to the Syrian National Coalition or any other groups in Syria, a full debate and vote will be held in Parliament and that in addition to this, if Parliament is in recess it should be recalled to facilitate this important debate."
The matter had to be "subjected to full parliamentary scrutiny and debate before we potentially become further embroiled in another Middle Eastern conflict.
"I appreciate that in some matters of defence, time does not always allow for a parliamentary debate; however I do no believe this constraint applies to this potential course of action."
Mr Bridgen has not named the other 80 MPs who signed the letter.
Responding for the government, House of Commons leader Andrew Lansley said the prime minister had been "absolutely clear" that, as with the intervention in the Libyan conflict in 2011, "any decision relating to the arming of the Syrian National Coalition or others in relation to Syria would be the subject of debate and an opportunity for a vote in this House".