The rest of the answers are clear. Yes it is unethical. But please allow me to take it another step further.
It is not good for you!
Here is a real example. I had temporarily joined in on a project in the very earliest years of the World Wide Web as an expert for which I was at the time. I had started back writing router code for what was to become the Internet back in the day and had spent a lot of time working with various Internet services such as the web and e-mail as well as for other products and competing networks. I was, at that time, uniquely qualified and had worked on many products and protocols and could do just about anything that was possible including writing protocol stacks and products specifically designed for a given purpose.
I found out within first one or two days that the government contracting company had modified my resume and presented me as an expert on a particular e-mail product for which I was indeed familiar. The promise was that I would be able to resolve a particular problem. The resume and promise was based upon a lie that I had no knowledge of. I got into the meeting and realized that the problem to be resolved was a well known bug that the e-mail software company was aware of and was resolving in the next major release due in a few months.
My dilemma was that there was no work-around for the bug, and that I was not able to modify the code directly. I was a systems internal engineer and could certainly reverse engineer the compiled code, make the modification, and recompile a working product, however, that would be illegal and take significant time. The contracting company promised that the problem would be fixed by Friday a timeline that was not only arbitrary, but also impossible. They made this promise to gain unique access to the contract. No other company was understandably willing to take on such an effort and excluded that portion of the work from their contract negotiation with a caveat as to the reasons why.
This not only put me in an impossible position, it also painted my in an ethical corner. After the meeting, I met with the contractor who hired me and stated that the promise was impossible to keep especially within the promised time-line. The company said do it anyway. I then went to the customer, Walter Reed Medical Hospital, whose care is critical to wounded veterans of war, and explained that what was promised was impossible. They appreciated my honesty and pushed back on the contracting company within minutes. During the fallout, I resigned and went home.
I called a lawyer immediately. Why? Because this was a major hit to my outstanding reputation. Afterall, I had full and complete access to Bell Labs, Dec Labs, and was a consultant to Digital Equipment Corporation, the Bell Corporation (the split into regional Bells with a parent company), Wang, IBM, Unisys, and many others supplying the government with critical services for which I was often called. One bad word about an individual would stop my ability to gain access to contracts forever and this was just a case that could do it.
In the end, my reputation did take a knock for being associated with the unethical misconduct anyway regardless of my innocence and lack of involvement. Why? Because this quickly became a fraud case for which I had to testify. I was able to regain my reputation once the fraud case was settled and I was able to present evidence of my innocence to the many who asked. And believe me, they all asked for about a year or so. This knocked me out of an entire industry for nearly two years. All well and good. I still had the trust of Digital and Bell who kept me very busy serving their customers and found a new niche anyway. That was the last of my government contracting and I never looked back.
I was lucky. Others may not have been. I have seen fraudulent contractor resumes float around all over the place painting the poor individual into a corner of explaining what happened. Some companies understand, most do not. The trust has been broken before you even arrived and you had no idea. Instead of a hopeful job interview, you walk into a difficult situation that you did not create. And believe me, this can last years!
My General Advice
Never walk into a situation unless you know you can 100% succeed. Know
the environment, know the problems to be resolved (and there are
always problems to be resolved), know that you have the skills to help
without reservation, and know the ethics of anyone you deal with to
the best of your ability. Trust is a major commodity within the IT
industry and likely others too. Without trust going both ways, you can
never have a rewarding and successful career. Trust me on that!