The Bureau of Labor Statistics has two types of data about work stoppages: Work Stoppages program data and the Strike Report.
The Work Stoppages program provides monthly and annual data of major work stoppages involving 1,000 or more workers lasting one full shift or longer. The monthly and annual data show the establishment and union(s) involved in the work stoppage along with the location, the number of workers and the days of idleness. The monthly data list all work stoppages involving 1,000 or more workers that occurred during the full calendar month for each month of the year. The annualized data provide statistics, analysis and details of each work stoppage of 1,000 or more workers that occurred during the year. The work stoppages data are gathered from public news sources, such as newspapers and the Internet. The BLS does not distinguish between strikes and lock-outs in the data; both are included in the term "work stoppages".
The Strike Report is a summary of strike activity during the Current Employment Statistics (CES) survey reference period, which includes the 12th of the month. See the Work Stoppages Frequently Asked Questions for more information on the differences between Work Stoppages and the Strike Report.