Curbs on mainland travel are due to be scrapped on Monday, April 26 but the Scottish Government has yet to announce when this will cover the islands, because of fears of increasing their low Covid-19 rates.
Up to a third of businesses are unlikely to survive an extension to the travel ban, according to the Scottish Tourism Alliance, which represents hundreds of island businesses.
It said its members had already suffered a “wave of cancellations”.
Chief executive Marc Crothall said: “Tourism is critical to our island economies and the impact of current restrictions has been severe.
“The seasonality of tourism in Scotland means it is absolutely vital our island communities are able to receive the same economic stimulus as the rest of the country, and the businesses that have been closed and unable to trade for so many months can be revived in line with the rest of the tourism economy.
"If businesses in our islands can’t follow the same approach as the mainland, the impact will be more severe than may be understood currently.
"It is particularly surprising from a [Scottish] Government that has extolled its legislation promising equal and fair treatment of the islands in everything it does.
"Businesses will lose trade to mainland businesses and people will choose to visit other destinations, leading quickly to business failure, significant unemployment and an economic and social crisis within our island communities.”
Emma Clark, vice-chair of Argyll and the Isles Tourism Co-operative, said: “To still be held in limbo is simply unfair and crippling.
"Some islands are losing £2 million a week in cancellations alone in favour of mainland destinations.
"It’s absolutely shocking when we are already at our lowest to leave us hanging on for clarity.
"We are losing all hope.”
Ms Clark, who owns the Glenegedale House guesthouse in Islay and chairs the Explore Islay and Jura marketing group, said: “We need to recover both health and economic-wise and have a short season to do this.”
Loganair, which provides most air links to the islands, shared the concerns.
Chief executive Jonathan Hinkles said: “We support the calls for clarity.
"I raised it with the cabinet secretary for transport [Michael Matheson] and was advised a decision may be within the next couple of weeks.
"As every day passes in which we could plan for the safe re-opening of island travel and tourism, it's a day of the summer lost, however.
"Clarity cannot come soon enough.
"The safe re-opening of tourism is possible, and we have advocated a testing regime at departure airports and ports as an additional assurance step.
"But I'm told constraints around ferry port infrastructure will preclude this happening - which is an unwelcome constraint.”
The Association of Scotland’s Self-Caterers said the islands must be given parity.
Chief executive Fiona Campbell said: “Our island tourism businesses, including many self-catering operators, are deeply concerned at the prospect of losing business due to any difference in travel restrictions between the islands and mainland.
“It is vital that the Scottish Government allows the islands to go forward in lockstep with the rest of Scotland so as to give the tourist economy the shot in the arm it sorely needs.
“To have any differences would result in an effective extension of the lockdown, which is the very last thing our members, and their businesses, need right now.”
CalMac, which operates ferries to the Hebrides, said it would continue operating at an average of 35 per cent of normal capacity because of distancing requirements.
Increased sailings under its summer timetable start on April 26, a month later than normal.
First Minister Nicola Sturgeon announced to MSPs on March 16: “We expect that from April 26, restrictions on journeys within mainland Scotland will be lifted entirely.
"However, if restrictions on socialising and hospitality are relaxed more quickly and significantly on the islands, there may be a need to retain some restrictions on travel to and from the mainland - to protect island communities from the importation of new cases.
"However, rather than impose that decision now on our island communities, we intend to discuss it directly with them to determine what arrangements they consider will work best for their circumstances.”
Ms Sturgeon said on Tuesday that an update on infection levels would be published “in the next few days”, which would “provide some more information about the changes we hope to make during April and May, and into the summer”.
A Scottish Government spokesperson added: “We know many businesses and some communities are keen to open as soon as is safe to do so, but that others are more nervous of the impacts of doing so.
"We want travel to get back to normal as soon as it is safely possible, but as the First Minister has set out, we must move very carefully to ensure continued suppression of the virus.
"If we open up too much, too quickly, then we risk a resurgence of the virus.
"We must also do this in a way that carries most support from island residents and communities, and will give them confidence and reassurance that it is safe for people to visit our islands, and also for islanders to visit the mainland.
“While we are engaging with island authorities, communities and businesses to better understand their views, keeping people safe remains key and we must all continue to follow expert public health advice.
"As we have done throughout the pandemic, we will apply and follow the ‘four harms’ [health and isolation, the NHS and the economy] process to consider what, if any restrictions might be eased for island authorities.”
A spokesperson for VisitScotland said: “Businesses and communities have been working together to ensure everyone is ready and supportive of opening, to restart tourism in a responsible way.
"It’s going to be a careful balance between the economics of restarting businesses, protecting jobs and ensuring communities don’t feel their vital resources are threatened."