The right-faction union attempted to derail the ALP's special platform conference with a last-minute injunction following complaints its numbers should be increased.

HWU secretary Diana Asmar ramped up her threats at the online meeting of delegates on Tuesday, reserving her right to challenge any decision made in court.

"This is not a proper, constitutional national conference," she said.

Health spokesman and left-faction heavyweight Mark Butler won overwhelming support to delete controversial parts of the HWU motion.

The initial motion noted private health providers should not be subsidised or supported.

"With a health system that depends so clearly on private general practitioners, private clinicians, in part private hospitals and private health insurers, I simply can't support a statement like that," Mr Butler told the conference on Tuesday.

The HWU also wanted a future Labor government to not award contracts in private health without guaranteeing the pay, conditions and jobs of public workers.

"Why can't we say yes we believe in our public system, we will protect it, we will not sell it to the highest bidder, we will not sell out our public health workers," Ms Asmar said.

Mr Butler also opposed part of the motion about contracting in state and territory hospitals.

But he encouraged the union to continue its campaign on that issue through Labor's state branches.

The federal frontbencher's amendment made a clear commitment to public provision as a central pillar of health policy.

Mr Butler was supported 352 votes to 22.

Australian Associated Press