The group Care Not Killing spoke out after a poll was released by My Life, My Death, My Choice earlier this week which showed that 69% of Scots would back a Bill currently going through Holyrood which would introduce legal euthanasia.
They have seized on the figures and pointed to a similar poll conducted in 2010, the last time MSPs discussed assisted suicide, which showed that support stood at 73%.
The campaign also claimed that polls can be misleading as people tend to back assisted suicide in principle but change their minds when how the process would work in practice.
A spokesman for Care Not Killing said: "The Bill will go before MSPs who do not make laws by opinion poll and who overwhelmingly voted against a similar Bill as recently as 2010.
"However, it is interesting to note the decline in support for assisted suicide since the last time it was proposed.
"In November 2010 much was made of the fact that around three quarters of people claimed to support that Bill."
The Bill would allow anyone terminally ill or suffering from deteriorating progressive conditions, who is over 16, could inform their GP of their support for the right to take their own life.
Their support would have to be made at least seven days before they could formally ask to end their life.
But Dr Peter Saunders, campaign director of Care Not Killing said: "The right to die can so easily become the duty to die and vulnerable people who are sick, elderly or disabled will inevitably feel pressure, whether real or imagined, to end their lives so as not to be a burden on others.
"Ms MacDonald's new proposals are effectively her old ones dished up again. I expect parliament to give them short shrift."
A My Life, My Death, My Choice spokesperson said both polls showed that support for assisted suicide had stayed broadly stable over the years.
He added: "The questions our polls was based on were very concise and referred specifically to the plan contained in the Bill.
"We wanted to make sure that the level of support we received was for the actual issue we were campaigning for."