As companies grow, they encounter issues that smaller firms don't. For instance, many employment laws, such as the federal Family Medical Leave Act, apply only to firms of a certain size or larger. As you grow, your employee policy manual has to grow with you. Simply knowing what's right isn't enough. When the majority of--or even all--employee supervision was handled by you or one or two trusted colleagues, maybe you could survive on faith in them and them in you. But as your company grows, you'll hire new employees and new supervisors, and that means you'll need to commit to writing exactly how employees ought to be treated and the behaviors your company won't tolerate.
Laws concerning sexual harassment are steadily evolving, and your policies on harassment in the workplace need to keep pace. For example, one recent ruling says that a company without a strong anti-harassment policy is likely to be held liable if one of its supervisors commits sexual harassment against an employee.
In general, anti-discrimination employment legislation is expanding to cover a larger group of employees. Along with gender, race, color, religious beliefs, national origin, age and disability, some jurisdictions protect employees who are discriminated against on the basis of appearance or sexual orientation. Your employees may be protected from any retaliation by you because they reported you for violating a law or regulation. Take note of federal, state and local laws regarding discrimination, and make sure their intent is clearly reflected in your employee policy manual.
If you're unclear about which laws apply to your small business or what to include in your employee manual, consult your attorney or an attorney familiar with U.S. labor laws.