This graph plots labor share (left) against the unemployment rate (bottom) since 1948 to 2ndQ 2016. (data at FRED)
The data points suggest a labor supply limit shown by the down-sloping red line. As labor share drops, unemployment tends to bottom out at higher levels.
The last 3 quarters are circled. Recent data is rising up the supply limit line.
If the limit holds, further declines in quarterly unemployment will call for more labor share.