Nearly three quarters of conservative people would be "unhappy" if an immediate family member were to marry someone who didn't believe in God.
The poll by Pew Research found that 73 per cent of "consistently conservative" people would be "unhappy" if an immediate family married someone who didn't believe in God.
This was far higher than the percentage who would be unhappy if their family member married a Democrat (30 per cent).
Even among those who described themselves as politically "mixed" and "mostly liberal", the percentages were quite high - 51 per cent and 41 per cent respectively.
Taking ideological spectrum, just under half of all Americans (49 per cent) said they would be "unhappy" with their loved one marrying an atheist.
Americans were generally indifferent about their close relative marrying a born-again Christian - just 9 per cent would be unhappy.
Even consistent liberals are generally indifferent, with only 27 per cent saying they would be "unhappy" about this.
Most were also not too bothered about a family member marrying a Republican, with 73 per cent saying it doesn't matter.
"Most Americans are comfortable with political diversity in their households," said Pew.