Unions are preparing a public show of strength over Labor leader Luke Foley at next month's party conference by flexing their muscles to secure blanket opposition to any increase in the GST.
The move, at Mr Foley's first conference as party leader, is being viewed as a backlash to his comments about being open to considering a GST rise in certain circumstances and determination to be independent of unions on policy matters.
Fairfax Media understands the right wing United Services Union is proposing that the conference adopts as Labor policy opposing any increase in the GST - a move that would bind all MPs to the position.
The motion is believed to state that "most fair minded people" believe the GST is a regressive tax which overwhelmingly affects low-income earners.
The USU was one of the main unions which expressed its concern over Mr Foley - a left faction member - being supported into the leadership over right wing rivals such as shadow Treasurer Michael Daley.
The left wing Australian Manufacturing Workers' Union is proposing that "NSW Labor does not support an increased in the Goods and Services Tax or moves to broaden the base of this tax".
Both proposals reference support for federal opposition leader Bill Shorten's campaign against an increase in the GST, which is being proposed by NSW and South Australia to federal Treasurer Scott Morrison.
But they are being widely seen as an assertion of authority over Mr Foley after his earlier statements.
In an interview marking his first year as leader, Mr Foley said he would consider supporting an increase in the GST from 10 to 15 per cent as long as the funds were used solely for health and education and to compensate low-income earners.
"If an increase in the GST would do two things - firstly, compensate people on lower incomes hit hardest by such a rise, but secondly, the revenue gains were ploughed purely into health and education provision by the states, well of course I'd look at it," he said.
However, he added that he didn't see "any willingness for that from the conservative side of politics".
The comment earned a rebuke from Mr Shorten, who said state leaders are under pressure over $80 billion in federal cuts to health and education funding but that a GST increase was "wrong".
Mr Foley has also declared he will not go in for "fake consensus" with trade unions on policy issues where the public interest is in conflict with union views.
Acting NSW Labor general secretary Kaila Murnain is understood to have been involved in a discussion about making the USU motion one of the main conference debates.
Asked about the motions on Friday, Mr Foley said: "I oppose the Liberals' regressive plan to raise the GST, as do my colleagues in NSW Labor."