I thought the parent was making a joke. Is this actually a thing in America? In Australia I have never seen this in any of my contracts.
Take a look over here to see a bunch of anecdotes about this very US based 'policy' https://old.reddit.com/r/antiwork/comments/15dvtwa/why_do_so...
This also goes directly along side that retail workers are NOT permitted to have chairs at a register, because of the similar reason (standing constantly excludes disabled and pregnant folk). And somehow sitting=lazy unless it's white collar work. We're allowed to be 'lazy'.