"Let us continue to pray and raise our voices in the private and public arena and in our wider community."
Bishop Campbell called on the Southern District Health Board and its management to reject a licence to perform abortions at Southland Hospital.
The board has been criticised over a lack of consultation on the issue, but has said it is satisfied with its approach.
The bishop's letter comes in the week the Government received a draft United Nations committee report urging abortion reform in New Zealand.
The UN's committee on the elimination of discrimination against women said it was concerned abortion remained criminalised in New Zealand.
Women needed the go-ahead from two certified consultants before they could get an abortion, which "nullifies their autonomy", and some women were undergoing illegal abortions that were often unsafe.
The committee called on the Government to review abortion law and practices with a view to ensuring women's autonomy to choose, to prevent women from having to resort to unsafe abortions, and to remove "punitive provisions" imposed on women who had an abortion.
Women's Affairs Minister Jo Goodhew said she had received the draft report earlier this week and would consider its recommendations.