Pauline Hanson has declared she will not support the Coalition government's tax cuts when federal parliament returns next month.

The One Nation leader, who carries two crucial Senate votes, said there were more important issues to be funded.

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"At this stage, no I'm not," she told Nine Network on Monday, when asked whether she would support the tax relief.

She nominated building a coal-fired power station and getting on with a 1930s plan to divert water inland as two higher priorities for her.

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Her opposition will make it tough for the government to pass its full tax plan.

Labor supports the first stages, for low and middle income workers, but at this stage is uncomfortable with the later parts which will flatten the tax rates schedule by mid-2024 and overwhelmingly benefit higher earners.

The government is adamant it will not split up the package.

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If it can't get Labor onside, it will need support from four of the six crossbenchers since the Greens also oppose the package.

But the other crossbench duo, Centre Alliance, holds a similar position to Labor with concerns that a softening economy might leave the country unable to afford the later stage of the plan without cutting essential services.