Adelaide's Catholic Archdiocese will enter the debate over South Australian abortion law reform, with a letter from the church set to be distributed to parishioners this weekend.

Key points: The Adelaide Catholic Archdiocese is opposed to changes to SA's abortion laws

The Adelaide Catholic Archdiocese is opposed to changes to SA's abortion laws A letter from the church describes the legislation as the "most radical abortion law in the country"

A letter from the church describes the legislation as the "most radical abortion law in the country" The proposed changes were introduced to Parliament last year

The pastoral letter from Apostolic Administrator Greg O'Kelly states the church's opposition to the law changes, which would remove abortion from the state's crimes act and allow for it to be regulated under existing health laws.

Greens MP Tammy Franks, who introduced the bill to Parliament, is due to complete her introductory speech at the end of February, with the legislation to be decided later this year through a conscience vote.

"This bill treats abortion simply as a medical procedure without moral significance," Bishop O'Kelly wrote in the letter, which has been supplied to the ABC.

"There is no need for a medical opinion or a doctor's involvement and no reason need be given for an abortion.

Bishop O'Kelly has sent a letter to Adelaide parishioners sharing his thoughts. ( Diocese of Port Pirie )

"It will be the most radical abortion law in the country."

However, Ms Franks rejected Bishop O'Kelly's advice to parishioners, and said similar laws had existed in the ACT "for some time".

"They're entitled to that point of view but they're not entitled to their own facts," Ms Franks said.

"The letter is not correct when it claims by treating abortion as a medical issue … that somehow no doctors and no medical opinion will be involved.

"In fact the opposite is true, it will be the medical opinion and the doctors and the medical professionals that guide abortion, not the criminal law."

Groups have started lobbying against legislation

The church correspondence also included another letter written by Adelaide gynaecologist Elvis Seman.

In his letter, Dr Seman criticised the creation of "health access" zones, that limit "the freedom to pray and offer pregnancy support near abortion clinics".

"As a church community, I believe that, with few notable exceptions, we have done poorly in supporting those women and their families facing an unplanned pregnancy," Dr Seman said.

Anti-abortion material was the subject of a complaint to the Electoral Commission. ( Supplied: Tammy Franks )

"They are left at the mercy of a health system which fast-tracks women to abortion and offers no alternatives.

"In addition, post abortion, we have not done nearly enough to support and heal the majority of those wounded emotionally, physically and spiritually.

"Their grief and suffering is very real and has been enormous."

The letter from the Catholic Church follows a complaint made to the South Australian Electoral Commission regarding anti-abortion flyers and a mobile billboard being used in the lead up to last week's state by-elections.

Other Christian-based organisations, including the Australian Family Coalition, have started to lobby since the legislation was introduced to Parliament late last year, asking members to call on their local politicians to vote against the bill.

The South Australian Abortion Action Coalition, the lobby group behind the legislation, is also circulating a petition to bolster support.