The State Government's move to allow religious schools to exclude students who do not share the same faith faces opposition when the legislation is debated in the Legislative Council.

Two years ago the Liberal Party failed to win support in the state's Upper House for its bid to give faith-based schools the right to make enrolment decisions based on a student's religion.

Now in government, it again seeks to grant schools an exemption from the Anti-Discrimination Act.

Independent MLC Ruth Forrest said her position had not changed.

"Where they're getting significant federal and state funding that all people contribute to there should be more of an open door policy," she said.

"I have real concerns about enshrining discrimination based on religion in our legislation any way."

Launceston MLC Rosemary Armitage said she believed schools should be able to say no on the grounds of religion.

"A lot of this makes legal what they've already been doing," she said.

Ms Armitage said small faith-based schools should not be forced to take anyone.

"Then they've lost the reason they actually came into being in the first place," she said.

Amendments have been flagged including ensuring schools can not discriminate on other grounds.

Debate on the proposed change begins later today.

Discrimination necessary when schools are 'oversubscribed'

Catholic Education Tasmania director John Mula told 936 ABC Hobart the change in legislation would streamline the process of selecting students who follow their faith.

"Currently the legislation means that school principals would need to apply to the anti-discrimination commissioner to discriminate on the basis of religious belief," he said.

"We have an issue in Year Seven next year where we're a bit oversubscribed.

"We would need to apply to the anti-discrimination commissioner to preference people of Catholic faith in that enrolment."

He said the schools would not see the exception as an opportunity to discriminate on anything other than religious belief.

"Essentially what we're trying to do ... is to try and preserve the faith and the teaching on which the school was built."