Dawn Strain and Martin Turner, a young unmarried couple living together in Queens, N.Y., have been fighting three times a week lately – but it’s not about sex, or family, or who should clean the house.

“We fight about money,” Strain said. “It’s definitely our biggest issue.”

Get ready to take sides: Couples can be at each other’s throats over how to spend, manage and invest their dollars.

Strain, 31, an entrepreneur and founder of professional networking group Long Island Elite, wants Turner to clean up the debts he accumulated in his previous marriage. Turner, a 30-year-old construction project manager, says he’s not ready.

A hard-nosed small business owner, Strain gets annoyed when her significant other wants to go out to eat, using up money they will need later on to buy a house together.

The couple face additional financial pressures because Turner has three children from his previous marriage. It costs Turner $200 in gas per weekend to pick up his kids from Connecticut and then drive them home.

“It creates a lot of stress,” Strain said.

They’re not alone. Financial planner J.J. Burns lately has been seeing couples blowing up at each other in his office.

One of his clients is fuming over his wife’s desire to spend $50,000 on plastic surgery.

“They told me they don’t have sex anymore,” Burns said.

Money long has been the biggest source of conflict for couples, numerous surveys show. But the tension is rising, as couples must now grapple with heavy credit card debt, rising gas prices, and ex-spouses and children from previous marriages.

Greg Kuhlman, a New York-based marriage counselor, says some of the mounting tension is a result of a power shift away from men and toward women.

About one-third of professional women earn more than their husbands and they are seeking more control over the purse strings.

“Every couple has power and control issues,” said William Bailey, one of the authors of the book, “You Paid How Much For That?!: How to Win at Money Without Losing at Love.’ “One of the sources of power is money.”

Also adding to the money feuds: Husbands and wives increasingly are keeping money secrets from each other, opening credit card accounts on the sly.

“It used to be hard to get a credit card without a spouse knowing,” said Ruth Hayden, who teaches couples how to agree on money matters. “Now you can open a credit card without anyone knowing about (it). People find out when they refinance a mortgage, so there are a lot of surprises.”

But there are ways to reach a consensus over money without tearing your partner’s hair out. The key, experts say, is planning and communication.

Turner, the construction project manager, said money fights were a key factor leading to his divorce from his first wife.

He’s determined to do better in his relationship with girlfriend Strain – and for good reason.

“If you’re fighting over money, you’re not having sex,” she said.