Is there any fundamental difference between resolutions for S-corporations and C-corporations?

Specifically, we are concerned with authorized signers. When owners want to add or remove signers, we would need to see new resolutions in both cases, correct? We have a customer that claims new resolutions don't have to be shown to remove or add signers for s-corporations.

I think they are basically the same. C-corps - the profits stay in the business. S-corps it is divided out among the owners for tax purposes. I thought that was the only major difference.

Whenever we had a change of authorized signers we always needed an updated resolution. The language in the resolution did not vary because it was still a corporate resolution that we used for C Corps or S Corps. Since the resolution reveals who can do what regarding the business account i would think you would need it updated.

Maybe they are thinking that the articles of incorporation don't need to be shown again?

You are correct that the major difference is how the corporations are treated for federal income tax purposes. They are still corporations and would follow all applicable corporate formalities for changing authorized signers on bank accounts (i.e., a new board resolution or action taken by designated authorized officer pursuant to an earlier board resolution).

There are additional differences between the two types of corporations. S corporations cannot have more than 75 shareholders and there are certain restrictions on who can be a shareholder. These limitations don't relate to the authority of corporate officers or what "proof" they need to give a bank to change authorized signers.