TMZ claims to have obtained a copy of the document and reports the agreement forbids attendees to discuss anything that happened at the wedding. Guests are expected to bring their identification to the wedding so they can sign the agreement before entering the ceremony.
Reports of the confidentiality agreement come one month after it was revealed that Union and Wade would not allow guests to bring cell phones, or cameras to the event.
Contract violators will reportedly be hit with a "hefty" fine.
The Think Like a Man actress, 41, and the Miami Heat star are scheduled to wed this Saturday in South Florida. The couple got engaged in December 2013 after four years of dating.