Nine bishops from the state of New South Wales have joined Sydney Cardinal George Pell to warn Catholics about voting in the March 26 state election for the Greens, who have gained "significant" influence.

In a statement March 17, the bishops said the Greens' plans to "attack" freedom of religion and conscience and promote abortion, euthanasia and same-sex marriage "give rise to grave concerns for the protection of human rights and human dignity."

The Greens could exercise "significant power over governments with only a few seats," the bishops said in the statement called The Green Agenda.

Two New South Wales bishops refused to sign the letter.

"The bishops need to take great care regarding intervention in the political process," Bishop David Walker of Broken Bay said in an interview March 18.

He said he supports the highlighting of key issues of concern.

"I do not believe . . . that attacking a particular political party serves to highlight these issues in the most effective way."

Lismore Bishop Geoffrey Jarrett, one of the letter's signatories, said the prelates were not telling people how to vote, but doing "what people expect of us" — being "watchmen on the tower."