Introduction Over the last several decades in the U.S., socioeconomic life-expectancy inequities have increased 1–2 years. Declining labor-union density has fueled growing income inequities across classes and exacerbated racial income inequities. However, the relationship between declining labor-union density and mortality inequities remains understudied.

Objectives Using Panel Study of Income Dynamics (PSID) data, we examined the longitudinal union-mortality relationship and estimated whether declining union density has exacerbated racial and educational mortality inequities.

Methods Our sample included respondents ages 25–66 to the 1979–2015 PSID with mortality follow-up through age 68 and year 2017. To address healthy-worker bias, we used the parametric g-formula. First, we estimated how a scenario setting all (versus none) of respondents’ employed-person-years to union-member employed-person-years would have affected mortality incidence. Next, we examined gender, racial, and educational effect modification. Finally, we estimated how racial and educational mortality inequities would have changed if union-membership prevalence had remained at 1979 (versus 2015) levels throughout follow-up.

Results In the full sample (respondents=23,022, observations=146,681), the union scenario was associated with lower mortality incidence than the non-union scenario (RR: 0.90, 95% CI: 0.80, 0.99; RD per 1,000: -18.7, 95% CI: -36.5, -0.9). This protective association generally held across subgroups, although it was stronger among the more-educated. However, we found little evidence mortality inequities would have lessened if union membership had remained at 1979 levels.

Conclusion To our knowledge, this is the first individual-level U.S.-based study with repeated union-membership measurements to analyze the union-mortality relationship. We estimated a protective union-mortality association, but found little evidence declining union density has exacerbated mortality inequities, although we did not incorporate contextual-level effects.