There is no difference. 'Ethics' is one of those words that is usually used in the plural form. Only exception I can think of is when you say 'work ethic'. Otherwise, 'ethics' is used mostly.
Since you've only posted a partial sentence, it's hard to tell which one is correct.
Whilst inclined to agree that it is difficult to distinguish any difference in meaning between ethic and ethics, I suggest there is a difference in use. Ethic tends to refer the values of a specific group, whilst ethics is perhaps more general. Ethic rather emphasises the way people think and behave, whilst ethics emphasises the rules.