As it was once explained to me by a lawyer some time back.
In the US dating in the workplace potentially falls under the case law of sexual harassment. The issue is basically the following:
- 2 of the companies employees are dating or even possibly get married working for the same company
- Then they brakebreak it off or divorce.
- Once that happens one of the parties involved can claim sexual harassment against the other and under some state and federal statutes the company may be held liable.
Given that potential scenario the companies discourage dating in the workplace to the point of making it a cause for firing an employee.
The dating of employees within the company is usually allowed by a special dispensation from Human Resources after a consultation with lawyers. And usually involves some paperwork to protect the company from scenario I described above.