LISBON — Portuguese opposition lawmakers appealed to a Lisbon court Thursday to block the planned auction in London next week of 85 paintings by Catalan artist Joan Miro owned by the cash-strapped nation.

The Socialist deputies said in a statement that the sale by Christie’s auction house would be illegal because the center-right government had violated rules on the classification of cultural assets while also ignoring “the immeasurable immaterial value” of the collection to Portugal.

Their move followed several parliamentary motions by opposition parties and a public online petition signed by nearly 9,000 people calling for the collection to be kept in Portugal.

“Despite the petition and motions against the sale, the government has decided to proceed, so now it becomes a court case,” said Luis Rego, spokesman for the Socialists in parliament, adding that he expected the court to deliver a ruling in time to block the sale.

Christie’s is due to offer the paintings in its Feb. 4-5 sales under the heading The Art of the Surreal and Impressionist/Modern.

The Miro collection became state property after Portugal nationalized the failed bank BNP in 2008.

The combined estimated value of the paintings is more than $48 million. The most highly valued, “Femmes et oiseaux (Women and Birds)” dating from 1968, is expected to fetch between $6.5 million and $11.2 million.

Portugal’s state culture secretariat had no immediate comment on the lawmakers’ move.

Christie’s confirmed that the sale remained scheduled for next week but declined to comment on the dispute in Portugal.