Citizens Advice Scotland is launching a nationwide survey of companies after concerns customers in more remote areas wait longer for parcels to be delivered and are charged fees that are substantially higher than elsewhere in the UK.
It comes after a study of individual consumers attracted 3000 complaints and evidence some island communities were having to pay a 500% mark-up on standard delivery of goods online. The additional charges are thought to apply to postcodes of around one million Scots.
The charitable organisation said businesses were being hit hard by the "postcode penalty". The survey, which is open until March 14 and is backed by Trading Standards and several local Chambers of Commerce, is aimed at uncovering the extent of the problem.
Margaret Lynch, chief executive of Citizens Advice Scotland, said: "Until now, we have mainly focused on the impact this has on individual consumers. But we have also been contacted by many businesses, particularly small business.
"High delivery charges can be absolutely devastating for them - both when sending and receiving parcels. We estimate that there are well over 20,000 businesses that could be affected.
"We want to assess how bad this problem is, so we are today opening a survey that is just for businesses. It's their chance to have their say and contribute their evidence to our campaign."
The earlier consumer survey found that a million Scots face surcharges, later delivery or are refused delivery altogether when they try to buy goods online.
At least 75% of delivery surcharges made by retailers applied to customers north of the Border.
More than half of 534 retailers investigated could not deliver to any Scottish island.
Ms Lynch said the organisation did not want "special treatment" but firms working out of Scotland wanted a "fair deal" on delivery.
The survey is at tinyurl.com/DeliveryCosts