Labour leader Jeremy Corbyn is meeting his shadow cabinet amid splits over whether to back air strikes in Syria.
Mr Corbyn is reported to be offering his MPs a free vote on whether to back strikes, which he opposes.
Shadow chancellor John McDonnell had urged him to offer a free vote, but his ally Diane Abbott said MPs should be instructed to vote with the leadership.
Ahead of the shadow cabinet meeting, Labour said 75% of party members it polled had opposed bombing.
The government is attempting to persuade MPs to back extending UK air strikes aimed at so-called Islamic State into Syria.
David Cameron says he will hold a vote on air strikes only if certain he has the clear support of the Commons, saying losing the vote would hand the Islamic State group a propaganda victory.
Mr Corbyn has written to Mr Cameron asking for a two-day debate to take place ahead of the vote.