There are not, unfortunately, many laws that establish or require employers to treat employees in certain ways. Discrimination laws (race, ethnicity, religion, age, disability, etc.) prevent employers from treating employees in a certain way due to their race, age, etc., but other than that and a few more (such as overtime, when paychecks must be paid, etc.) private employers (meaning those that are not government owned) are mainly free to establish employment policies.
There is no federal law that requires private employers to even offer breaks for food, bathroom, or other needs at all. Some states do have meal/rest break laws. The MN Dept. of Labor & Industry indicates that employers must offer these rest/meal breaks and these are the employee rights. As long as an employer provides the required breaks, they may then put in place work policies to better manage employees and work time. Unless a policy is applied unfairly (only used for some employees) or may violate a person's right under a discrimination law (such as if a person's disability, under the Americans with Disabilities Act) requires them to use a bathroom or go outside more often) those policies will normally be permitted. You can contact the MN Department of Industry & Labor directly as indicated here to learn if any state cases or other regulations may have, however, established that employers cannot require employees to ask for permission to use the bathroom.
Declarations by the UN are not necessarily "law" in the United States (see here). Also, the UN Declaration while adopted by the U.S. does not requries specific actions or laws, it only requires nations to work toward observing human rights. It is not a law that puts requirements in place for U.S. or state laws.
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