The following graphs are the result of my own calculations of monthly microdata from the Current Population Survey. They detail the level of labor strike activity through the proxy of workplace absences caused by labor disputes. The time series starts in January of 1976.
Labor Dispute Absences by Month
This graph shows the percentage of employed people who answered that they were absent from work in the prior week due to a labor dispute. The spikes generally coincide with big national or regional labor strikes involving large numbers of workers. Place your cursor on the graph line to get a detailed number for a given month. [Spreadsheet]
Average Labor Dispute Absences
This graph answers the following question: on an average month in the given time period, what percentage of the employed workforce said they were absent from work in the prior week due to a labor dispute? This graph is not interactive. [Spreadsheet]