Union membership has been on the declines for decades. However, union wages have remain stable. The Bureau of Labor Statistics reports that on average, in 2019, union workers earned roughly $1,095 per week, while nonunion workers earned closer to $892. Experts point to the contrast of low membership and high wages to being the product of labor reduction in historically union dominated industries such as manufacturing.
See "Union Enrollment has Declined for Decades, But Union Workers Still Earn 19% More", Abigail Johnson Hess, CNBC, February 22, 2021