It's pretty well established that unions increase wages for their members, at least in the US. This boost is known as the "union wage premium." Now, it appears there might be a union marriage premium as well.
In the impeccably titled paper, "Marrying Ain't Hard When You Got A Union Card?", in this quarter's issue of the peer-reviewed journal Social Problems, Berkeley's Daniel Schneider and Columbia's Adam Reich attempted to isolate the effect of union membership on marriage rates. They use the National Longitudinal Survey of Youth's 1979 cohort. That survey follows 9,964 people who were 14-22 in 1979 (that is, born in 1957 to 1964). Schneider and Reich track the share of respondents who got married through 2004, so the study looked at the probability that 14 to 22 year olds got married by age 40 to 47.
They find a relationship for men, but not for women: "Approximately 17 percent of men who transition to marriage are covered by collective bargaining agreements as compared to 14 percent of men who do not marry." They don't think that union membership on its own causes the increase in marriage rates — by, for example, signaling to prospective partner that one has a steady job with good compensation.
Instead, Schneider and Reich think it's likelier that union membership makes people, on average, higher-earning, likelier to have health insurance, more stable in jobs, etc., and those changes account for the difference in marriage rates between members and non-members. The relationship between those factors and marriage is much better established.
Bonus finding: contra anti-feminists' arguments that women's increasing incomes are undermining marriage, Schneider and Reich's data suggests that women who work more and have health insurance are likelier to marry.
Thanks to Tyler Cowen for the pointer.