Having a work ethic means being disciplined and hard-working among other things. But I'm hard-pressed to see this as being part of the notion of ethics in the usual or philosophical sense.
Who coined the term? It's hard not to believe it's relatively recent.
Is having a 'work ethic', in itself, in fact, ethical?
Let's start taking the Protestant work ethic as an example.
First, where does the Protestant work ethic come from:
the notion developed that it might be possible to discern that a person was elect (predestined) by observing their way of life. Hard work and frugality, as well as social success and wealth, were thought to be two important consequences of being one of the elect.
But, what does it mean to be "one of the elect?"
"According as he hath chosen us in him before the foundation of the world, that we should be holy and without blame before him in love: Having predestinated us unto the adoption of children by Jesus Christ to himself, according to the good pleasure of his will,"
Ephesians 1:4-5
(There are many other passages used by Protestants as justification for the idea of predestination, but many follow the pattern of not just being chosen, but being chosen to fit into the mold of Jesus).
So, to be of the elect means that one is empowered to behave in a Christ-like manner. So then, the protestant work ethic is ethical to the degree that one believes to act Christ-like is ethical.
While usually considered a "Protestant" idea, within Christianity the (Catholic) Benedictine Monks also have a tradition of taking work ethic seriously:
Idleness is the enemy of the soul; and therefore the brethren ought to be employed in manual labor at certain times, at others, in devout reading.
In both cases, there is a similar sentiment about how the work ethic relates to the soul.
I think having a work ethic is not necessarily ethical, but it can be consistent with ethics in regards to self-development and virtue. I disagree with "Having a work ethic means being disciplined and hard-working" and rather think that everybody has a work ethic regardless of how disciplined and hard-working they are.
I think it's more like people with less discipline who are lazy having a poor work ethic in contrast to people who have more discipline and are hard-working having a strong work ethic. Prudence consistently being the number one virtue for many philosophers implies that in terms of enlightened self development that the more regularly, consistently and harder one works in this regard the further one will get in self-development. In this context one could conclude that a strong work ethic is a virtue and that laziness is a vice.
Also in Aristotle's definition of virtue he says that all virtue is a medium on a continuum of excess and deficiency, so one could say that being a control freak or over achiever could be the excess, and laziness the deficiency, with the virtue of a strong work ethic residing in the correct balance.
From a general philosophical point of view, a statement about principles of work ethics (or any other particular ethics) would be relative and dependent upon its philosophical assumptions.
Philosophy providing more general and absolute meaning of purpose, and right and wrong can proceed to determine ethics for particular areas of life, e.g. work ethics, family ethics, research ethics, etc.
For example if cheating or betrayal is established as a moral wrong, then it would be also wrong to cheat in all areas of life, provided that the premise is not conditional or override-able.
But if contributing to an immoral cause is immoral (like serving a tyrant or criminal tycoon), then it may follow that 'betrayal' of the superior would be even moral in this context.
Therefore particular ethics are very much contingent upon more general universal ethics.
