According to Google AI, an F-7 Notice is "a mandatory, legally required form filed with the Federal Mediation and Conciliation Service (FMCS) by unions or employers to initiate collective bargaining, indicating the intent to terminate or modify a contract 60 days before its expiration."
The US government uploads Excel spreadsheets of all records of F-7 notices, which includes data of the target company and the labor union involved, on their website: fmcs.gov/resources/documents-and-data. Each table is a specific month of the year, and each row represents one collective bargaining dispute between a company and a trade union
This can be used to find active trade unions in your local area, as well as the companies they're disputing with, since the table includes street addresses.