Spanish art collector Baroness Carmen Thyssen will move the Thyssen museum to another part of Madrid in case the proposed building works will be started on one of the city's most emblematic streets.
The baroness said a widening of Prado Boulevard to five lanes from three would damage the Thyssen-Bornemisza Museum, of which she is patron, and overwhelm visitors with traffic.
"I definitely would ask the collection to be moved to another museum in Madrid because of the damage that can be caused" Thyssen told a press conference. "I don't know why they want to do it, to take away the painting rooms to such a wonderful museum like this, to damage it."
The plans, drawn up by Portuguese architect Alvaro Siza, are meant to make the street next to the Prado Museum, opposite the Thyssen Museum, more accessible to pedestrians. The museum houses valuable paintings collected by the baroness' late husband.
In May, when officials revealed that mature trees on the boulevard would be uprooted and moved, the baroness led hundreds of people in a protest against the plan.
The Spanish-born Thyssen acquired the title of baroness when she became the fifth wife of wealthy Swiss industrialist Baron Hans Heinrich Thyssen-Bornemisza.
The Spanish government agreed to house the late baron's art collection, one of the richest in the world, in 1993.
The museum, along with the Prado and Reina Sofia museums, is one of Spain's most popular tourist attractions.