At the weekend, the Glasgow Shettleston MSP was criticised for saying clinics “push abortion without laying out the pros and cons”.
In an email to campaign group Back Off Scotland, which seeks to implement buffer zones around abortion providers to push anti-abortion vigils further away from patients, Mr Mason said he had attended one of the events to speak to the people there.
He went on to say he believed abortion was “seldom essential or vital”.
Tweeting about the subject at the weekend, Mr Mason said clinics did not always ask women how they feel.
The First Minister was asked about his comments on Monday, as she spoke to journalists while visiting a new NHS 24 building in Glasgow.
She said: “I disagree with John Mason on the issue of abortion.
“I am a very passionate believer in a woman’s right to choose and I think attempts to take that right away, whether it’s in the United States or any attempts to undermine that right here, are wrong and I disagree with that.
“I also believe women exercising the right to abortion should be able to do so free of intimidation.”
Those who wish to protest abortion should do so outside parliament rather than hospitals, she said.
Ms Sturgeon was asked about Mr Mason’s statement that some clinics were “pushing abortion without laying out the pros and cons”.
She said: “I think that is wrong. I don’t think that’s the case.
“I don’t think any woman takes a decision to have an abortion lightly.
“And secondly, medical professionals take their duties very seriously and make sure that they do what is required to bring about a decision that is a fully informed one.”
Lucy Grieve, the co-founder and director of Back Off Scotland, had earlier responded: “John Mason’s false claims are incredibly dangerous and ignorant.
“This is the same elected official that admitted attending anti-choice protests at Scottish hospitals.
“He clearly has no idea what goes on during an abortion, and his comments are offensive to abortion providers and their patients.”