Okay, lets take a look at this one.....
Q1) "A Casino called my boss about an NSF check they were holding that I had written."
A1) What EXACTLY did they tell your boss??
Q2) "Now I'm having some problems at work."
A2) EXACTLY what types of problems are you having?? Are they directly related to the phone contact?? What makes you think that they are??
Q3) And finally, the kicker: "Is it legal fora Creditor to call my boss and do this?"
A3) Yes. The only prohibition that MIGHT have been valid would be the FDCPA, but that only applies to 3rd party debt collectors. There are simply no federal laws that apply to the creditors direct contacts. Further, these rules of contact only apply to consumer debts.... and gambling wouldn't qualify.
Lets look at your 'other' unmentioned issue.... the check itself:
"Sections 6-08-16 to 6-08-16.4 of the North Dakota Century Code provide both civil and criminal penalties against persons who passes bad checks.
Any person who passes a check which is dishonored within 14 days upon presentation, because of insufficient funds in, or credit with, the bank, he may be subject to criminal charges of an infraction if the amount is not more than $100, a class B misdemeanor if the amount is more than $100 but not more than $500; and a class A misdemeanor if the amount is in excess of $500. (6-08-16(1).) If a person willfully issues a check with knowledge that he does not have an account with the drawee bank, he is guilty of a Class A misdemeanor. (6-08-16.1.) A repeated offense may subject the maker of similar act to a conviction of a class C felony. (6-08-16.2.)
In a civil action, the maker of the dishonored check may be liable for collection fees or costs not to exceed $20.00, and civil penalties of the lesser of $100 or three (3) times the amount of the check. If a collection agency recovers any additional charges, it must reimburse the original holder of the check bank charges for such dishonored check not in excess of $2.00. (6-08-16(2).)
A written notice of dishonored is not mandatory prior to any action filed by the holder of a dishonored check. If a written notice of dishonored is sent by the holder, it may be made by return receipt or by an affidavit of mailing signed by the individual making the mailing."
Source:
http://www.lawdog.com/states/nd/sta2.htm