Presumptive tax facility withdrawn

Apropos the news item appearing in the Press regarding the unilateral decision of the government to rescind the declaration made by the manufacturers of goods for opting to the Presumptive Tax Regime (PTR) on July 6, 2005, through Circular 01/2005 dated July 5, 2005.
As a professional accountant, I would like to comment the wrong manner in which the same has been handled.
The Income Tax Ordinance, 2001, under section 153 allowed the manufacturer of goods apart from others to opt for the Presumptive Tax Regime where the tax deducted at source being 3.5% of the gross turnover, if deducted, was deemed to the full and final liability of the tax payer.
The Federal Government through the Finance Act 2005 has now withdrawn this option for the manufacturers in a way that the law was never there on the plea that the manufacturers were concealing the tax through this option and their tax incidence if charged under normal tax was higher than in the PTR option.
My question to the law-making authority is that if the manufacturers opted for this selection under the law by filing an irrevocable declaration for 3 years that even if their profits are less they would be liable to pay tax on their gross sales, how can the Government withdraw the lawfully-filed declaration retrospectively by accusing the payers of concealing tax and threatening to retrieve the already lost revenue. There has to be some respect for the law, at least for the law prepared by them.
I would also like to remind the tax authority that manufacturers don't plan for one year as our government. New projects in the commercial arena, and also the multinational companies make out feasibility of the project for 5-7 years period with certain assumptions, in which tax incidence is of foremost importance. If our government tends to change the tax laws every year how can we claim to the foreign investors that our policies are consistent. What is BOI doing.
It is my humble request to the tax authorities to review their decision in a way that the tax payers can have faith in our policies by upholding the already filed declarations upto their term.