It's important to note that the tax disclosure laws won't give detailed information; only headline numbers. But it's more detail than we've been getting so far. More importantly, once that information is freely available the onus is on companies to explain it. Accounting firm tax partners say some of the c-suite are already gearing up for the PR war. EY tax adviser Glenn Williams has said there are now boardroom discussions about how to voluntarily present "in straightforward language" an accurate picture of their tax affairs to the public. The Tax Justice Network ignited a debate when it released its report last year – which had its faults – finding most companies paid well below the 30 per cent corporate tax rate. It sparked a Senate inquiry that will see companies appearing in public to explain their "tax minimisation" strategies.

In a submission to that inquiry, the Uniting Church has presented FOI documents noting that of the 2168 entities identified by the ATO as reporting more than $100 million in total annual income, and therefore affected by the disclosure laws, 30 per cent did not pay tax in 2012. The tax disclosure laws will force them to answer, why not? If the company paid zero tax on billions of dollars of profits by shifting them into low-tax nations, the company will have to publicly explain why. If they declared losses, and got big tax breaks for it, they will have to publicly explain why. If they are claiming "losses" and paying zero tax because they paid out compensation to asbestos victims – one of the extraordinary revelations in James Hardie's submission to the inquiry – they will have to explain why.

The ATO numbers on companies claiming losses and getting tax breaks is staggering. Its submission said that in "2012-13 about 149,000 companies utilised $18.1 billion in prior year tax losses to offset against current year taxable income". If one was to multiply this by the 30 per cent company tax rate (assuming they paid tax at the headline rate) it means they claimed $5.4 billion in tax breaks, all legally. A host of ASX 200 companies including Echo, Mirvac, Oz Minerals, Transurban, Lend Lease, Toll, Rio Tinto, Woodside, Asciano, Newcrest, Orica, Challenger, and many more detail in submissions to the inquiry how they have a great "working relationship" with the Tax Office and most claim their tax affairs are of little concern to the agency. A former ATO officer, Martin Lock, explains in his submission, how already the line between tax avoidance and tax minimisation is blurry. In its recent annual report the Tax Office confirmed that it is settling claims worth millions of dollars with large businesses. Lock says the loss of Tax Office expertise following 3000 job cuts, together with complex "grey law" and restrictions on the type of information the agency can collect from companies, means that billions of dollars of revenue is at stake.

At the same time, the government is now looking to redesign and rewrite tax laws. But who is helping Treasury rewrite these laws? The lobby group representing multinationals, the Corporate Tax Association, and a host of other tax lawyers representing large companies. Lock says there's concern changes could be pushed "to meet specific needs of their clients". Further "greyness introduced into laws leaves open room for taxpayers and their advisers to negotiate favourably with the ATO if interpretative disputes happen to arise", he says. As the Senate inquiry continues, it's worth politicians thinking about how public discussion can assist, rather than hinder, the ability of governments to collect revenue.

As Lock says, "the important question, is not what instances of tax minimisation are unlawful but rather which ones are unacceptable". Being able to figure that out starts with having greater transparency.