They can, but it is more of a personal matter that is best left unshared. The best option would be to let your boss/leader tell the rest of the employees. You wouldn't want to be a gossip now would you? :P
An employee will be fired if they are not suitable for the job. They may be unsuitable because they do not work hard enough, do not get along with other staff or may have violated company rules
An employee can be fired for any unprotected condition. If the employee is a union member, the union contract will specify how and when one could be fired. If not a union member, an employee could be fired for any reason other than one that is forbidden by law or that is contrary to established company policy. An employee handbook would have to state that piercings, or some general category including piercings, are a protected condition, before being fired for them would be forbidden. In some workplaces, where sanitation is important, where disease risk is unusually high, or where employee appearance is important, many kinds of piercings may be specifically forbidden.
An employer say you are still working for them after they have fired you only if they continue to pay you and there is a contract that limits your ability to obtain other employment for a time.
Yes, an employee in an at-will employment situation can be fired for any reason other than a reason specifically prohibited by law. They can legally fire someone for wearing red shoes if they want to. Ethical? No. Legal? Yes.
Slander or Defamation of character.
No, you cannot be fired by someone other than your boss, unless your employment contract has stipulated that you can. You also need a letter from your boss stating the reasons why you have been fired. Your boss's authority is decided only by her superiors, not by any statute. Almost no US workers have contracts limiting who can fire them. No employee need to be informed of the reasons for a firing, unless a contract specifies that.
Pretty much the answer is that in the US you can be fired for just about anything. Most employment in the US is "at-will", which means if your employer gives you requirements (such as calling in) and you fail to perform them, yes he can fire you. Even if it's the first time. Unless your employment contract/employee handbook specifically says you can not call in once and not get fired. In other countries, particularly in Europe, employees have more protection, and the answer might be different.
Certainly. An employer has no liability for defamation unless it broadcasts falsehoods about a person. Broadcasting facts about an employee's firing violates no law.
Yes. any disrespect to other employees, or the company can be considered misconduct.
It depends on the state. Some states are "at will" work states, which means the employee can quit at any time for any reason, and an employer can let an employee go for any reason at any time. If you're serious about the question, it's unlikely you would get fired for that, but if you were, the employer would probably give some other more reasonable sounding reason.
Costco has been sued by its employees in the past. In 2012, a former employee of Costco sued the company for unlawful dismissal and unpaid overtime after being fired when he tried to organize other employees to bring attention to safety concerns.
In most cases, there needs to be a written policy about this matter. Sometimes an employee will come off suspension and still work their, other times, pending investigation, an employee may be fired. Suspension length differs depending on the situation.