Corporate giant Wesfarmers Ltd said yesterday that the federal government's proposed resources super profits tax could hurt its operational value in the coal sector as chief executive Richard Goyder stressed that it would be hard to estimate the new tax's actual financial impact on the company.

Wesfarmers operates Coles supermarkets and Bunnings hardware outlets around the country, with further business interests in coal mining, LPG processing, fertilisers, chemicals and insurance.

Mr Goyder said that estimating the effects at this time will be quite difficult as the impact of the proposed tax would be different based on different commodity prices and a different exchange rate in the future.

He added that the government should withdraw its plan to levy more tax on the resource sector since its implementation "would decrease the value of not only our investments but prospective investments in the resources business that we're involved in."

Mr Goyder pointed to the fact that the resources industry has been paying its due share and a case in point is that Wesfarmers' resources division paid some 41 percent of profits in corporate tax and state royalties last year.

He also said that the government would need to reconsider its plan to impose the resource rent tax retroactively as this would result to further losses on earlier investments made with consideration on tax regimes in effect at that time.

Mr Goyder revealed that the company sat down with a government consultation group last week and he characterised their tax discussion "was quite constructive and certainly the panel felt that Wesfarmers' submission had been well thought through and prepared."

He admitted though that talking with politician on the tax issue was far from his mind and with all the debates raging on the matter, he would rather focus on "hard work needed to be done to come to a better conclusion that is in the long-term interests of all Australians."

In the end, Mr Goyder said that he is optimistic that the government would stick to sound governance and all its hallmarks "so they can look at things, can listen to feedback and listen to a consultative process and make appropriate changes."

He noted that for most of the people he had conferred with, all have expressed concerns that the proposed tax measures was generally flawed and must be revised and corrected first should it see actual implementation.