"The Real Housewives of New Jersey" star made the revelation on Wednesday night's episode as she and her husband had a heated argument over the phone ... while Joe was in ICE custody.

Teresa shouted, "You made me sign a prenup, okay?" and later claimed in a confessional he asked her to sign it a week before they tied the knot ... much to her dismay. She said, "I just felt when you love someone, you don't do that."

Teresa went on to say she considered calling off the wedding over it, but decided instead to sign the prenup under one condition -- she made him add a clause stating if he ever cheated ... the prenup was off.

As you know ... rumors of Joe cheating have swirled for years, but Teresa recently said she never caught him in the act.

It's unclear if Joe even added the no-cheating clause, though, because Teresa also said she never even read the prenup!

Joe followed up Teresa's bombshell with one of his own ... he fired back at her by claiming he never wanted to get married in the first place.

As we reported ... the couple decided to call it quits last month after 20 years of marriage. That length of time is important in terms of the prenup because many provide if the couple is married for a certain period of time -- usually, 10 years -- the prenup is either nullified or it enhances the rights and financial entitlements of the person who was forced to sign it