Thousands of protesters are expected to turn up outside Downing Street to urge the Prime Minister to change his stance.
The group said the protest has been called due to the "imminent threat of bombing of Syria by British forces", for which a vote is expected to take place as early as next week.
Labour leader Jeremy Corbyn is chair of the Stop the War coalition, and has a long history of pacifism. He has opposed air strikes in Syria, which has threatened to tear apart the shadow cabinet, with senior Labour front benchers threatening to resign if Corbyn forces them to side with him.
The demonstration will take place between 12 noon and 2pm, with the organisation calling for similar marches in over 30 cities and towns nationwide.
The group said: "There is already bombing in Syria, conducted by the US and French forces. Its net effect has not been to weaken ISIS. The cumulative effect of 14 years of western bombing in the region has been to increase the scale and spread of jihadi terrorism." It added:
When Russian bombing of Syria began, nearly two months ago, David Cameron and Barack Obama warned that it would be counter productive, increase the threat of terrorism and create instability in the region.
Exactly the same applies to UK and any other bombing.
In parliament on Thursday, Cameron made the case for air strikes to be extended into Syria, as dealing with the threat posed by the so-called Islamic State should not be "outsourced", with many of the UK's allies calling it into military action.
Former Labour leader and Prime Minister Tony Blair has also said that Cameron can rely on the support of "many Labour MPs".
Meanwhile, Stop the War coalition recently came under controversy after reportedly silencing Syrian people at an event it organised to debate the prospect of air strikes in Syria.