Prime Minister Julia Gillard said the issue of refunding royalties remained on the table with premiers and Treasurer Wayne Swan said the tax would be reviewed.

''We will look at the performance of this tax, in light of prices, in the normal way, by our Treasury and, of course, by our tax department,'' he told the House of Representatives.

It follows the government's reluctant admission that the tax had produced only a fraction of the projected revenue.

On Friday, Mr Swan revealed it had raised $126 million in the first half of the financial year, well short of $2 billion predicted for the full 12 months.

The government had already allocated the funds to increasing the superannuation guarantee from 9 per cent to 12 per cent and the abolition of tax on super contributions for the low paid.

The government blames the shortfall on low iron ore prices last year and the belligerence of the states in increasing mining royalties that have to be refunded to miners under the terms of the minerals resource rent tax.

The tax's failure dominated Parliament on Monday and frustrated Labor's attempts to move to its preferred ground of industrial relations through changes to the Fair Work Act to improve protection for vulnerable workers.

Government questions centred on extending the existing right to ask employers for work flexibility to women subject to domestic violence and parents returning from parental leave.

Labor wants to draw the Coalition into an industrial relations debate.

Opposition Leader Tony Abbott stuck with the economy and the mining tax failure. He asked if Ms Gillard retained confidence in Mr Swan in light of ''the Treasurer's failure to deliver the promised surplus this financial year, his failure to collect more than 10 per cent of the promised $9 billion in mining tax revenue, and his failure to deliver on his promise to create a least 500,000 new jobs in two years''.

He asked whether she would rule out design changes to the tax.

Ms Gillard replied that the role of state governments in hiking royalties was ''reckless'', indicating the GST Distribution Review had advised the situation was ''unsustainable and undesirable''.

''Interestingly enough, the opposition that has always criticised an efficient profits-based tax in minerals but has gone tick, tick, tick to Liberal royalty increases around the country,'' she said.

Shadow treasurer Joe Hockey dashed hopes of soon releasing costed policies after obtaining advice from the new Parliamentary Budget Office that the most reliable budget baseline will not be known until the Pre-election Economic and Fiscal Outlook report.

This brought a withering response from Mr Swan. ''This is a deeply deceptive ruse from the Coalition to hide the impact of their policy proposals from the Australian people,'' he said. ''The idea that the Coalition can refuse to release what any of their policies cost until deep into the campaign is unprecedented.''

The Greens introduced a private member's bill designed to plug the royalty refund and raise an extra $2.2 billion over the forward estimates.

Sponsor Adam Bandt described the MRRT as a dud, slamming the government for taking more from single parents through welfare tightening than from wealthy miners.

Government backbencher Doug Cameron criticised the interplay of royalty increases and their refund by the Commonwealth.