After the PSOE victory in March 2004, President José Luis Rodríguez Zapatero entrusted Caldera with one of the most important responsibilities within the executive committee: to lead the Ministry of Labor and Social Issues, an office he assumed on 18 April 2004.

Key labor reforms: Caldera raised the minimum wage to 600 euros/month, built consensus with social agents for labor reform as well as social security that allowed for the creation of more jobs with permanent contracts and improved payments to the neediest groups, at the same time he guaranteed the future of the system by making early retirement more difficult.

Additionally, he brought forward the independent contractors statute and put a plan in place to reduce workplace accidents.

Key social reforms: Caldera created a new right, the right of dependent people to get assistance, raised paternity leave days from four to fifteen.

This foundation's mission would be to create new ideas and projects for the party with the objective of staying abreast of social change and offering up to date solutions.