Federal Reserve Bank of Cleveland:  Labor's Declining Share of Income and Rising Inequality:

Labor income has declined as a share of total income earned in the
United States. This decline was caused by several factors, including a
change in the technology used to produce goods and services, increased
globalization and trade openness, and developments in labor market
institutions and policies.

One consequence of the labor share decline has raised concerns. Since
labor income is more evenly distributed across U.S. households than
capital income, the decline made total income less evenly distributed
and more concentrated at the top of the distribution, and this
contributed to increase income inequality. In this Commentary,
we look at how the labor share decline has affected income inequality in
the past, and we study the likely future path of the labor share and
its implications for inequality.