THE Morrison Government will guarantee no State or Territory is worse off under its GST plan in a move that appears set to get the long-awaited deal through the Parliament.

The Liberal and National party rooms this morning signed off on the proposal from Treasurer Josh Frydenberg.

Under the proposal, a guarantee will be made that no State or Territory can be worse under the overhaul of the GST allocation system as it is slowly introduced between 2021-22 and 2026-27.

As the full change to the GST system is introduced, the Productivity Commission will review it to ensure it is working properly.

If a State or Territory is left worse off beyond 2026-27 then extra top-up payments from Canberra will be considered.

The Government had been facing pressure from some of its own MPs, particularly those in NSW and Tasmania, about the GST system changes that will ultimately deliver billions in extra GST payments to WA.

The new system will see first a 70 cent then a 75 cent floor introduced as well as an overhaul of the allocation system.

Canberra will pour $7 billion in top-up payments into the GST pool to ensure States and Territories are not left worse off through the transition period.