Fourteen packaging firms were worried enough to meet at Glasgow Airport and declare their opposition to the levy proposed by Liberal Democrat Mike Pringle.
The Carrier Bag Consortium (CBC) attended that meeting and convinced the companies there were no environmental benefits to the tax.
So all parties agreed to campaign publicly against the idea and admitted there was a big risk politicians would be persuaded to vote for it.
CBC spokesman Peter Woodall, who made the presentation in Glasgow, said: There is a level of serious concern that ill-informed politicians may introduce the tax, with negative environmental effects.
The main output of the meeting was that the businesses realised there were no environmental benefits to the tax and agreed to act in opposition to it.
Travelstock Packaging director Ron Keenon said: This constitutes no more than yet another stealth tax. It is unjustified, obscene and even goes as far as contradicting Government figures on reuse.
Look at the time and the expense our politicians are wasting on this junk science.
The CBC outlined eight reasons why it opposes the tax, including fears of an increase in litter and theft.
The organisation insisted plastic bags were more environmentally friendly to transport than paper ones, had a high reuse rate and took up little room in landfill sites.
Pringle is considering a tax of around 10p per bag, which the CBC says works out as a 2,000% rise an equivalent charge would make a newspaper cost £12.
Woodall added: A bag tax would effectively remove the highly convenient, secure and hygienic method of carrying groceries home and disposing of kitchen waste, while leaving everyone to purchase replacement bin liners.