Shoppers with disabilities have been excluded from some websites and apps needed during lockdown to buy essential items or services, research has found.
Features such as drop down menus are awkward for people with sight problems or other disabilities and some websites are impossible to navigate.
The Covid-19 crisis has "turned back the clock" for disabled people, campaigners say.
The Purple Tuesday project highlights the spending power of this group.
Firms have been missing out on vital revenue because disabled people have been unable to access their websites, and the new lockdowns and restrictions across the UK have the potential to rekindle the problems, the campaign says.
Mike Adams, founder of Purple Tuesday, said: "National and regional lockdowns have shone a very bright light on the approach of organisations to their disabled customers.
"With 22% of the population being disabled, meeting their customer needs is a huge economic and social opportunity for businesses."
Born with a physical disability, Mr Adams uses dictation and a pen held in his mouth to operate his laptop computer.
Billions in 'click away' losses
The awareness day aims to highlight the swift shift to online booking services owing to the pandemic, which had come "at the expense" of disabled people.
Among the issues being raised are:
- Online forms which are difficult for people with sight loss to navigate using screen readers
- Product information failing to make clear whether an item is suitable for disabled people
- Reports of some rail websites that do not have facilities to book priority seating online
- Missed delivery slots leading to difficulties collecting from depots
One report suggested that inaccessible websites were costing UK businesses up to £17.1bn, as disabled online shoppers clicked away from their services last year.
Justin Tomlinson, minister for disabled people, said: "We know this has been a challenging time for our high streets and businesses.
"It is more important than ever to unlock the spending power of disabled people and I would urge businesses to do just that and reap the rewards."