WCAG guidelines break accessibility issues down into three levels. Level A issues are the most urgent and include problems that can severely limit a disabled visitor’s ability to navigate or use the website. Level AA issues tend to be more rooted in functionality, addressing areas where improvement is needed to give disabled users the full experience of a site. (Level AA is considered the target standard for most commercial websites.) Level AAA issues are the highest standard, fine-tuning and expanding on issues identified as Level A and AA. While it is an excellent goal, full Level AAA compliance is likely beyond the reach of most websites.

People with disabilities that affect their sight, hearing, or mobility may have difficulty accessing certain parts of websites and other online properties unless certain accommodations are made. Just as businesses may need to make adjustments to their physical location so that disabled customers have easy access to the premises, companies may need to adjust certain aspects of their websites so individuals with disabilities can take full advantage of all the features and services.
The gray area is a matter of scale and purpose. If you have a small business which serves as specific market it's a good idea to make the site as user and disability friendly as possible. If, however, your market serves segments with a likeliness to have various handicaps or disabilities you should address that with an ADA Compliance review of the site. Also consider the scale and purpose of an organization. Publicly traded large businesses need to concern themselves more than a single location family owned retailer and if someone sues your flower shop because the text was too small or didn't have "image alt tags" causing them distress... That's pretty frivolous and would likely not stand.
The Americans with Disabilities Act (ADA) was first passed in 1990. Twenty years later, the US Department of Justice released an update called the 2010 ADA Standards for Accessible Design. These standards cover the design of physical spaces and have been interpreted to include web locations as well, so it can be difficult for the would-be accessible website designer to use them.
The large number of people who have disabilities, coupled with the challenges that they face, is one of the reasons that the Americans with Disabilities Act (ADA) was passed in 1990.² As its name suggests, the ADA is designed to protect individuals with disabilities in the United States. The ADA essentially makes it illegal for any government entity or business to provide goods and services to the general public without ensuring that the entities are accessible by people with disabilities. In today’s digitally driven world, many businesses fail to follow web accessibility best practices. In fact, this is why the Supplemental Advanced Notice of Proposed Rulemaking (SANPRM) was created by the U.S. Department of Justice (DOJ). To ensure that they are implementing digital accessibility best practices, organizations are encouraged to use the WCAG 2.1 technical requirements.³
Aloha Tatiana! I wish your questions had straightforward easy answers – and if you are government funded it kind of is. (See here: https://www.ada.gov/websites2_prnt.pdf) if you are not government funded, this is something that is currently being debated in the legal system. That being said, the WCAG 2.0 guidelines are a good set of guidelines to help protect yourself if you feel you should. (You can see more on WCAG here: https://www.yokoco.com/find-out-how-to-make-your-website-compliant/)
The need to make websites, mobile apps, and other online properties accessible to all is only going to increase as time moves on. Smart business owners will do well to get in front of this issue and make sure that their websites are ADA compliant now so that all their customers have the equal access to the resources they offer. Not just because they want to avoid a lawsuit or government action, but because it’s the right thing to do.
While the influx of the dot.com world eliminated the need for brick-and-mortar locations for all stores (think eBay or Amazon), all of the above categories typically had a headquarters, if not multiple locations where one could visit and interact.  This would ensure a unique experience, often depending on the individual needs of the visitor. For instance, when visiting a municipal building or institute of learning, a variety of methods are available to get to higher floors (stairs, elevators, ramps and escalators).

That’s good news if you are one of the many Americans who have a visual, hearing, or mobility disability that makes it difficult to access some information on the web. If you are a business owner who hasn’t made provisions to ensure that your website and other online assets are ADA compliant, you could be looking at a host of legal and financial penalties.

For most businesses, the need for ADA web compliance means they will need to make at least some adjustments to all of their online marketing strategies. For instance, if your company provides tax preparation services, all of the tax forms you provide for customers to download would need to meet accessibility standards. Any online tax preparation services that you offer would also need to be configured so they meet ADA standards, as would your mobile app.

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Additionally, in February 2018, Congress passed the ADA Education and Reform Act, a bill designed to make it harder for disabled Americans to sue businesses for discrimination. Republican lawmakers who wrote and passed the bill argue that the law will help curb “frivolous” lawsuits, while opponents have argued that this law will gut the ADA, essentially giving businesses little reason to follow the ADA guidelines at all.
I recently finished a training in ADA compliance for websites. It was illuminating and daunting, as I realizated that there’s a lot of work to be done. It also reiterated—in no uncertain terms—a gospel I’ve been preaching for several years now. Sites need to be accessible for everyone on every platform. Previously I was just focusing on responsive sites (sites that reformat for the device used, such as a phone or tablet.) Since responsive sites are de rigueur these days, I’d like to focus on your site’s accessibility…can it be accessed by people with disabilities? This includes screen readers and other technology. It’s not just a nice thing, it’s a civil law.
Yes, all websites must have hand rails in the rest rooms, ramps in lieu of front porch stairs and elevators with doors wide enough for wheelchairs to be easily loaded into them. Seriously though, ADA only covers Americans, and the Internet is hardly just an American institution. Besides, browsers can already be configured to override the web designer’s pre-configured fonts, font sizes, font and page and page background colors, etc, to make it much easier to read. Also, the big 3 Operating Systems (MS Windows, MAC, and Linux) have text-to-speech programs which will allow the computer to read...
As you’ve probably figured out by now, the answer is no, because it’s not at all clear how or even if ADA rules will be applied to any particular website. Still, it’s generally a good idea to err on the side of caution. Many states have adopted their own accessibility laws, and the volume of accessibility-related lawsuits filed against websites has ballooned in recent years. Plaintiffs have been more successful in these suits than ever before. With no clearly defined regulations to follow, it is probably not worth it for most companies to gamble that a court will rule in their favor.
Poorly designed websites can create unnecessary barriers for people with disabilities, just as poorly designed buildings prevent some people with disabilities from entering. Access problems often occur because website designers mistakenly assume that everyone sees and accesses a webpage in the same way. This mistaken assumption can frustrate assistive technologies and their users. Accessible website design recognizes these differences and does not require people to see, hear, or use a standard mouse in order to access the information and services provided.