The initiative, promoted by the party in the capital, primarily aims to provide local authorities with legal tools to ensure that large property owners and those with high-value homes contribute more equitably, thereby reducing the tax burden on working families.

The proposal comes at a time when housing prices in Madrid have increased by 110% over the last decade. Furthermore, 56% of used home purchases are for investment, and 1% of owners with more than 15 flats control 24% of the rental market.

The party denounces the current "fiscal injustice" in the capital, where a 4-million-euro home in the Salamanca district pays the same tax rate as a 200,000-euro flat in Puente de Vallecas. They argue that the mayor's linear tax cuts have resulted in "fiscal gifts" totaling 1.28 billion euros, primarily benefiting properties with higher cadastral values.

Key aspects of the bill include making the IBI progressive, similar to income tax, so that the 10% of highest-value properties pay more, allowing for a reduction for the remaining 90%. It also seeks to penalize large holders who accumulate more than four homes with a coefficient of up to 1.6, and to increase taxation for properties owned by companies, vulture funds, or corporations up to a maximum of 1.3, to encourage their return to residential use.

For its implementation, the reform would require a simple majority in the Congress of Deputies, as it is an ordinary law. This measure will be presented at the next Cibeles plenary session on April 29, with the goal of including it in the 2027 Fiscal Ordinances.