"I've got to protect my stuff," the Being Mary Jane star matter-of-factly told the ageless Arsenio Hall on The Arsenio Hall Show Monday night.
Union, 41, has made it clear she's hoping to avoid repeating mistakes she made when her first marriage, to NFL star Chris Howard, ended in divorce in 2005.
"The biggest difference between this and the last marriage will be a prenup – at my insistence," she bluntly told Hall as the audience giggled. "The reality is, I've never seen Dwyane balance a checkbook."
Wade, 32, proposed to Union in December after presenting her with an eye-popping engagement ring. Two months later, it appears wedding planning is in full-swing (she even cops to adhering to a porn diet to stay in shape), and Union vows it won't be anything like her first nuptials.
"The last time, I just wrote checks," she admitted. "I was working, I had a wedding planner, and I just showed up and was like, 'Ooh, that's nice. Who picked that out?' "
This time, she says, she's determined the keep things small, which means no bridesmaids and a pared-down guest list.
"There's a lot of people who think they're coming," she said, calling Wade the "executioner" who is not afraid to cross people off the list. "If you're not about us and we don't both have a relationship with you, you're not going to make it."