(CBS Local) — Is there really a crime worse than cheating on your partner? According to a new survey, nearly a third of Americans say “financial infidelity” was even more harmful to their relationships than being unfaithful.

CreditCards.com’s poll of 1,372 adults, all of whom were all in a relationship, found that 31 percent of responders believe hiding a credit card or bank account from their spouse or partner was a bigger betrayal than cheating.

“You don’t know what the other person is spending money on,” said Sonya Britt-Lutter of Kansas State University. “Are they spending it on another person, or are they spending it on something else that pleases them in a way that you’re not pleasing them as a partner or spouse?”

The study added that around 15 million Americans are currently in a live-in relationship where their partner doesn’t know about all of their finances. That number is up from an estimated 12 million CreditCards.com announced in February of 2017. Another nine million have reportedly committed “financial infidelity” in the past.

“Keeping secrets in your relationships is never a good idea,” the website’s senior industry analyst Matt Schulz said, via CBS News. “What starts out small tends to build. Spending $25 without consulting your partner may seem incidental, but when those purchases become more frequent or if the amount grows, it can wreak havoc on your accounts and your budget.”

The survey also found that people earning less were more likely to be hiding some financial secrets, with Americans earning less than $40,000 being the most common financial cheaters in the study.