The first event that led to the passage of federal labor laws was that progressives started to call for reforms. Lewis Hine and Marie Van Vorst were very important reformers.
Lewis Hine took photographs of children working and exposed it to the public, while Marie Van Vorst was a writer who wrote about her terrible experiences and worked for reforms. She wrote "The Woman who Toils".
The second event that led to the passage of federal labor laws was lobbyists working to influence legislators. Florence Kelly worked against long hours and the tiny minimum wage. She also worked against sweatshops.
This is a sweatshop in the 1890's.
The third event that led to the passage of federal labor laws was individual states passing labor laws. For example, Arizona, Arkansas, Florida, Mississippi, and Oklahoma had the right to not support a union enacted in their constitutions.
The final event was Congress passing federal labor laws. For example, the Clayton Act (which focused on price discrimination, price fixing and unfair business practices) and the Davis-Bacon Act (a federal law that makes it required to pay for for local prevailing wages on public work projects for laborers and mechanics).