Despite what you are being told here so far, you actually can record any conversation.
The only problem is, in this instance and most others, you only get to play that card once.
After that, the collateral damage will vary from scenario to scenario, and at UPS they may take the position of discharge.
In the end, you will be far better off establishing your credibility through your body of work, rather than trapping a "rat" into saying something they regret on tape.
Get a reputation of taping people, and nobody will ever talk to you again.
Would you blame them?