The ADA itself holds different organizations to more/less stringent standards based on a host of factors, government funding being a major one. Government agencies themselves are usually held to the most severe standards. That said, while ADA has adopted WCAG as the defacto standard, from what I’ve seen it appears they’re going with AA compliance as the most reliable one. That said, we’ve done work with some organizations who’ve chosen to comply with AAA in an effort to be as buttoned up as possible from an accessibility and experiential perspective. We’ve also worked with some who have tighter budgers and aim for level A compliance and have a more “react and repair” mindset when they discover anything in their site that is giving someone hardship from an accessibilirt standpoint.
In an August 2016 case involving the University of California Berkeley, the DOJ ruled that the public university was in violation of ADA Title II (similar to Title III but it instead applies to government organizations) because their YouTube channel’s videos didn’t include captions for hearing impaired visitors. The DOJ found this to violate the ADA as deaf users did not have equal access to the online content.
Decided by the US Supreme Court in 2002, this case  held that even requests for accommodation that might seem reasonable on their face, e.g., a transfer to a different position, can be rendered unreasonable because it would require a violation of the company's seniority system. While the court held that, in general, a violation of a seniority system renders an otherwise reasonable accommodation unreasonable, a plaintiff can present evidence that, despite the seniority system, the accommodation is reasonable in the specific case at hand, e.g., the plaintiff could offer evidence that the seniority system is so often disregarded that another exception wouldn't make a difference.
Tennessee v. Lane, 541 U.S. 509 (2004), was a case in the Supreme Court of the United States involving Congress's enforcement powers under section 5 of the Fourteenth Amendment. George Lane was unable to walk after a 1997 car accident in which he was accused of driving on the wrong side of the road. A woman was killed in the crash, and Lane faced misdemeanor charges of reckless driving. The suit was brought about because he was denied access to appear in criminal court because the courthouse had no elevator, even though the court was willing to carry him up the stairs and then willing to move the hearing to the first floor. He refused, citing he wanted to be treated as any other citizen, and was subsequently charged with failure to appear, after appearing at a previous hearing where he dragged himself up the stairs. The court ruled that Congress did have enough evidence that the disabled were being denied those fundamental rights that are protected by the Due Process clause of the Fourteenth Amendment and had the enforcement powers under section 5 of the Fourteenth Amendment. It further ruled that "reasonable accommodations" mandated by the ADA were not unduly burdensome and disproportionate to the harm.
This was a case filed before The United States District Court for the Eastern District of Michigan Southern Division on behalf of the Michigan Paralyzed Veterans of America against University of Michigan – Michigan Stadium claiming that Michigan Stadium violated the Americans with Disabilities Act in its $226-million renovation by failing to add enough seats for disabled fans or accommodate the needs for disabled restrooms, concessions and parking. Additionally, the distribution of the accessible seating was at issue, with nearly all the seats being provided in the end-zone areas. The U.S. Department of Justice assisted in the suit filed by attorney Richard Bernstein of The Law Offices of Sam Bernstein in Farmington Hills, Michigan, which was settled in March 2008. The settlement required the stadium to add 329 wheelchair seats throughout the stadium by 2010, and an additional 135 accessible seats in clubhouses to go along with the existing 88 wheelchair seats. This case was significant because it set a precedent for the uniform distribution of accessible seating and gave the DOJ the opportunity to clarify previously unclear rules. The agreement now is a blueprint for all stadiums and other public facilities regarding accessibility.