The correct answer is:
Hiring strikebreakers.
Since the late 1800s, hiring agencies providing anti-union services has been an option for employers. In 1874, Charles Pratt's Astral Oil Works, a company owned by John D. Rockefeller, started buying refineries in Brooklyn to lower competition. Around the same time, the coopers' union, representing the workers who made the barrels that held the oil, faced Pratt's attempts to cut back on some manual operations. Pratt busted the union, and his strikebreaking practices became popular among other refineries.
