what regulatory references can I use to disallow this practice?

If you are talking about a bank official accepting a deposit outside of the bank building, you could discuss the need to have a mobile branch license for such activity. Management should certainly understand the physical security risk associated with such a practice.

To add to Brenda's - also check with your insurance carrier. It may not cover this.

i am concerned when bank officers, making customer calls to the place of business, accepting deposits from the customer...

Then I believe the above are valid points to consider.