Opposition parties have welcomed a Constitutional Court judgment that rules regulating the introduction of bills in Parliament's National Assembly are unconstitutional.

The Democratic Alliance (DA) said on Tuesday it had consistently complained that the process was openly politicised.

"Virtually every proposal we have made has been thwarted without due consideration or adequate justification," DA chief whip Watty Watson said in a statement.

Examples were the proposal to prevent the government from doing business with companies owned or managed by public office bearers or political parties, and the proposal to better regulate the allocation of national lottery money.

Watson welcomed the judgment and congratulated the Inkatha Freedom Party and its MP Mario Oriani-Ambrosini, who took the matter to the Constitutional Court.

"[We want to] thank them for taking the initiative to fight for something that will benefit all members of Parliament and all political parties in the future," Watson said.

In his judgment earlier in the day, Chief Justice Mogoeng Mogoeng said the rules which stated that permission was needed were inconsistent with the Constitution and were therefore invalid.

Oriani-Ambrosini had tried to introduce a bill in the National Assembly in 2009. The speaker of the National Assembly refused him permission to introduce it because he did not follow the rules.

Oriani-Ambrosini challenged the constitutional validity of the rules in the Western Cape High Court. This was dismissed. He then applied to the Constitutional Court for leave to appeal the judgment.

The Constitutional Court declared that those provisions of the rules which imposed, reinforced, or were inextricably linked to a permission requirement, were constitutionally invalid.

Oriani-Ambrosini said the judgment was a "game changer".

"[It] takes South African democracy onto a new and higher level of engagement, which is finally on par with all established democracies of the world," he said in a statement.

"This judgment removes what was one of the major shames in our democracy."

Oriani-Ambrosini said the judgment opened the door for laws to be drafted and introduced in Parliament by MPs who were not Cabinet members or deputy ministers.

The Freedom Front Plus congratulated Oriani-Ambrosini.

"The Constitutional Court has confirmed that the rules, which impede the right of MPs to introduce legislation, do not adhere to the constitutional imperative which embodies that right," FF Plus chief whip Corne Mulder said in a statement.

"This confirms the right of all MPs who serve different communities to introduce legislation which would protect those communities' interests."

Mulder said it was not just the African National Congress' right to unrestrictedly introduce legislation.