Are their any guidelines on being able to limit customers withdrawing large amounts of cash in a government crisis?

Nope. Business and security decision.

Read your account agreements. Maybe the authors thought to reserve the right to limit cash withdrawals in one way or another.

If we don't have anything in our account agreement aren't we restricted from limiting withdrawals other than on savings deposits? I haven't seen anything in the Banking Act or bulletins that have come out saying we can withhold customer's funds from them.

There is no requirement that you hand a customer currency and you need to manage your cash to allow you to service all of your customers. This is an emergency after all and that is true even when it is not. If they want their money, there is nothing wrong with limiting cash and handing them a cashier's check for the rest.

Not that it changes anything, but you might point out that the deposits to these accounts weren't 100% currency, so why should you have an obligation to return the funds in cash!

Interesting, but there is no legal support for either statement is there? Honestly, when (if) this ever ends we will amend our Deposit Account Agreement to give us the right to withhold funds in an emergency to avoid a lawsuit. Right now, it would be nice if the regulators or Congress would grant emergency authority to do so, don't you think?

Make a case and present it to all the members of Congress who represent the districts where you have offices. The FDIC was born out of the need to calm people and prevent runs on banks. Temporary measures like cash withdrawal limits are reasonable and designed to dampen panicky behavior. Who knows, in today's environment, anything is possible.