Asking potential employees if they are pregnant, married, plan to become pregnant, have children already, etc... is illegal under US law as well. Common German practices like asking for a photograph on an application or CV or asking about a prospective employee's religion are also usually illegal in the US, as it's pretty hard to think of non-discriminatory reasons an employer would need that information.

Asking previous employers about their experience with an employee, however is not illegal. It's usually not illegal for them to say something negative if it's true, though some businesses are conservative about what they will say out of fear of being sued for slander. Accessing public court records or news stories about criminal cases and using that information for employment purposes is usually not illegal. Asking prospective employees if they've been convicted of serious crimes is usually not illegal.