Spain's Constitutional Court is expected to rule on the nation's 2005 gay marriage law.

The Madrid-based El Pais reported that the 11-member court will meet on Tuesday and is expected to vote on an appeal filed by the conservative Popular Party (PP).

The PP filed the legal challenge to the law soon after Socialists approved it seven years ago. The PP returned to power in elections held late last year.

The court has postponed its ruling several times and its makeup changed slightly after conservatives returned to power. However, most analysts believe the court's progressive majority will uphold the law.

PP leaders have said that the government would abide by the Constitutional Court's ruling on the law.

Nearly 20,000 gay and lesbian couples have married since such unions became legal in Spain.

Spain was the third country behind the Netherlands and Belgium to legalize gay nuptials. Canada followed suit 17 days later.

(Related: Spain's Jose Zapatero says he's proudest of gay marriage on his way out.)