Members of the Scottish Parliament will today hear evidence on proposals for a large retailer levy.
Scottish finance secretary John Swinney, who proposed the levy, will answer questions before the Local Government and Communities Committee.
The Scottish Government plans to increase business rates for large retailers, which could see them paying up to 15p in the pound a year extra.
The levy is expected to raise around £30m but it won't affect pubs.
The Scottish Retail Consortium (SRC), which represents retail businesses in Scotland, is challenging the intent to single out a small number of firms for extra taxation.
Retailers have warned of the threat the levy poses to future job creation and investment in Scotland.
Swinney will be expected to justify the proposals.
"It is extremely worrying that there is so little clarity on a key budget proposal so late in the day," said SRC director Fiona Moriarty.
"The issues we urge the finance secretary to address are ones which we have been seeking explanations for since this misconceived tax was first announced.
"The consequences for Scotland of this tax are extremely serious. There will be fewer large retail stores opening in the future and fewer existing stores will be expanded.
"That means a reduction in future job creation, both at the major retailers and at businesses which support them.
"Last week members of the Scottish Parliament's Finance Committee made it clear they felt there were flaws with the proposed large retailer levy.
"Their report on the draft budget specifically highlighted the contradiction between the measure's intention to support town centres and the fact it will increase taxes for some key town centre stores. This is not the only anomaly which needs to be explained.
"The contribution the retail sector makes to the Scottish economy is substantial and will grow, providing this anti-retail levy is rejected."