Final answer:
Opposition from employers restricted the growth of labor unions during the last 1800s. Business owners mistrusted organization efforts and used various tactics to crush unions.
Step-by-step explanation:
The factor that restricted the growth of labor unions during the late 1800s was d) Opposition from employers. Business owners mistrusted organization efforts and used various tactics to crush unions, such as open shops, strikebreakers, and yellow-dog contracts. They capitalized on widespread anti-union sentiment among the general public. Additionally, cultural and racial barriers and the belief in a strong work ethic hindered effective unionization.