Directly employed mineworkers in big open-cuts are still earning a typical $150,000 a year, while their colleagues employed through labour hire companies say they sometimes earn less than $100,000 for the same work.

The disparity between the two types of employment is causing friction in some workplaces, with big companies like BHP Billiton and Rio Tinto demanding substantial cost cuts from their contractors, regardless of whether they supply labour, machinery or other services.

The growing disquiet has come to the surface over negotiations at BHP's giant Mount Arthur mine near Muswellbrook.

One Mount Arthur contractor said the difference in hourly rates was bad enough, but contractors were not paid the traditional industry coal production bonus, worth anywhere from $400 a week to more than $1000 a week.

They were also sent home without pay in wet weather, while direct BHP workers were paid ''to sit in the shed''.

In a statement to the Newcastle Herald, BHP Billiton confirmed it had changed labour hire providers last July as part of a drive to ''reduce costs and improve operational efficiency''.

The former contract holder, Tesa Mining, lost to Chandler Macleod, which took over Tesa's Mount Arthur contract workforce.

BHP and Chandler Macleod both declined to comment on the situation, with each saying it was a matter for the other to speak about.

Construction, Forestry, Mining and Energy Union district president Peter Jordan disputed the size of the pay gap between direct employees and contractors.

Mr Jordan said the Mount Arthur contractors would be on more than $100,000 a year.

But the Herald has seen various Mount Arthur pay slips showing Tesa was paying a flat rate of $46.50 an hour, or $84,630 a year for the industry standard 35-hour week.

Mount Arthur workers said Chandler Macleod cut their pay rate to $40 an hour, or $72,800, before the union stepped in and pushed the rate to $43 an hour, or $78,260.

The most recent official earnings figures show NSW mineworkers earning an average of $2785 a week, or $144,820 a year, compared with average Australian full-time earnings of $1542 a week, or $80,184 a year.

Although Chandler Macleod declined to comment, its website said a recent vote on the enterprise agreement had been successful.

The company said the agreement would cover its employees at any mine from the Central Coast to the Queensland border.

It said Mount Arthur employees would be paid a flat rate of $41 to $43.84 an hour, ''an increase of 7per cent or more from your current ordinary flat rates of pay'' at a time when ''coal prices are under significant pressure'', making ''your rates competitive against other labour hire providers in the Hunter Valley''.

One labour hire manager told the Herald the situation had ''come full circle'' since the peak of the coal boom, when people were leaving full-time employment to chase even bigger money in short-term contracts, where truck drivers at Gunnedah, for example, could earn $170,000 a year.

Now, people were hanging on to full-time jobs when they could, but the more that the contract labour rate was cut, the greater the gap between the two.

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