Some places of employment run policies, policies such that one must have a certain "professional", so to speak, kind of image in order to represent that specific company. Companies have the right to want to look and not look a certain way.
This professional look can be achieved for people with tattoos. Their tattoos can be covered with clothing such as suit jackets and long sleeve shirts. A company is allowed to maintain a certain look, but this does not mean they can tell an employee they can't work because they don't meet the visual requirement. If they're an asset to the company, it makes no sense to cast them away based off of their appearance.
Certain ones cannot be covered up and that goes for piercings as well. A person can have all the knowledge and stamina required for a postion but like it or not people profile just by looks and if a boss does not like your appearance and you are not willing to change for the company your not getting hired.
For tattoos that cannot be covered with clothing there is a special cover-up made for tattoos that can be used to conceal them. As for piercings, they can be temporarily taken out for the day and replaced with retainers (plastic, nearly invisible jewelry that is placed in the piercing to keep it from closing. It is not impossible to keep them concealed in the workplace so having them shouldn't be an issue.
Some people have tattoos on their face and some have them on their neck. Others have full sleeves and chest pieces. How are those people going to cover them especially in the summer time when temperatures are hot? They will make themselves uncomfortable for the likings of a job and that discomfort will effect their work ethic. Nobody puts their all into their daily regimen when they are feeling uncomfortable.
As I said before, there is makeup that is made specifically to cover up tattoos which can be used for the face as well. Here is a video demonstrating how effective it is . As for the heat, most offices have air conditioning. Even in the summer businessmen must dress in button down shirts and long pants, so their tattoos wouldn't be exposed anyway.
There may be ways to cover up tattoos but who wants to sit there an hour before work putting heavy make up on to go to work then having to wash it off every night. It will become tedious and eventually expensive. As for piercings there may be plugs that substitute for the earring itself but if you have an eyebrow ring, nose ring, lip ring or any piercing around your face, that hole is still going to be noticed and look unprofessional in the employers eyes.
The only places where tattoos can't be covered with clothes are the face, neck, and hands. Applying the cover up to these areas will take no longer than 20 minutes, and its virtually the same as a woman applying and taking off her make up every day. The cover up retails for $37, and a little goes a long way. The price is a bargain for the quality of the product. As for the piercings, I myself have had my lip and nose pierced, and the holes are so small you can't even notice them unless you're looking closely at my face. These holes can be covered with concealer as well, making them nearly invisible.