Both organisations promote cycling; both fear a helmet law will reduce the amount of cycling in Northern Ireland.
The Cyclists (Protective Headgear) Bill was narrowly approved by the Northern Ireland Assembly in January and is now being scrutinised by the Environment Committee.
The CTC/ Sustrans petition against the proposal can be signed by anyone in the UK, whether they live in Northern Ireland, England, Scotland or Wales.
CTC and Sustrans have been careful to explain that they are not "anti-helmet". Instead, they point to a plethora of evidence showing that Northern Ireland would see a sharp reduction in the number of people who would cycle, should the bill become law, creating a knock-on effect on public health, quality of life, congestion and the environment.
Explaining CTC's stance, Roger Geffen, Campaigns and Policy Director, said: "This bill may be well-intentioned, but it will deter vast numbers of people from cycling. At a time of mounting concern about obesity and climate change, scaring people into car-dependence is bound to shorten more lives than helmets would possibly save. I'd recommend our petition to everyone who enjoys cycling. With their support we can defeat this fundamentally flawed bill."
Sustrans' Northern Ireland Director Steven Patterson said: "We share the wish of the supporters of this bill to improve the safety of cyclists but there are many better ways of doing this, such as giving every child on-road cycle training or reducing speed limits to 20mph in residential areas."
Along with the petition, CTC and Sustrans will submit a portfolio of evidence to the legislative committee.