In-laws are apparently to blame for more than half of married couples' rows.
A study has found that 60% of married people in Britain blame their in-laws for relationship rows and around one in five would divorce them if they could.
The top reasons for tension include in-laws giving unwanted opinions, partners taking their parents' side, and disagreements over how to discipline grandchildren.
Almost a third of those surveyed described their partners' parents as "interfering", with those who clashed with in-laws exchanging cross words on average once a month.
Two thousand married Britons took part in the study by law firm Slater and Gordon, which said issues with extended family are often cited as a reason for divorce.
The research found in-laws caused arguments in 60% of marriages, while 22% said they would divorce them if they could.
One in five husbands and wives said their marriage suffered from lack of privacy caused by their spouse's parents dropping in unannounced or coming to stay.
Slater and Gordon said the rising cost of living means many adults borrow money from parents for large purchases, such as buying a house, and 19% of those surveyed believed in-laws expected more of a say in their lives in return.
The firm's family law specialist, Rupi Rai, said: "Economic pressures mean people are becoming much more reliant on their parents for financial help, to get on the housing ladder, to help them out if they lose their jobs or in some cases for very personal reasons such as to pay for fertility treatment.
"That can lead in-laws to take much more of an interest in how their money is being spent, which a child may understand, but their partner may not and may find uncomfortable."
Some 28% of those surveyed claimed the problem had got so bad they had considered splitting up and around one in 10 had done.
More than a quarter said they would never have gone down the aisle if they had known how bad the problem would be.
About 22% said they hid their true feelings from their partner for fear of upsetting them, with 36% revealing that they made up excuses not to see in-laws or went out when they visited.
Ms Rai said: "It's understandable to want to avoid confrontation, but it's rarely a solution. Often your in-laws may not even realise that what they're doing is causing offence.
"Addressing problems at the start is better than letting them linger and allowing resentment to build.
"The best advice is to try and put yourself in your in-laws' shoes and if you still think you're being treated unfairly, explain your concerns to your partner and them in a calm and rational way.
"We see relationships that have broken down after years of issues like these and the situation may have been different if they had been openly discussed at the time they arose.
"If you're recently married, remember that this is new territory for them too. They have to adapt to having a daughter or son-in-law the same way you have to adapt to them."