Is there any regulation that restricts banks from issuing a debit card for a MMDA?

No, but be prepared for excessive transactions if you do.

If you do give them the debit card, you should make them aware of the limit on those types of transactions, and how they are aggregated with other 'covered' transactions so they know the rules.

This is one of those "but we've always done it that way" issues. You can issue a debit card here, but that would seem to encourage transactions and Georgia nailed it. You make it convenient and it will be used. If the card isn't distinctive from another one, or if they can select the MMDA from a list and do so accidentally, you'll have more enforcement accounts to deal with and to track. Plus, if you charge a fee on excessive transactions, you'll get blasted for those. The purpose on a MMDA isn't to do transfers. It is supposed to be more stable money. Put them in a NOW.

Thanks everyone for your input!!