Parlamento del Mercosur (Spanish)
Parlamento do Mercosul (Portuguese)
The Mercosur Parliament is the parliamentary institution of the Mercosur trade bloc. It is composed of 81 representatives, 18 from each member states - Argentina, Brazil,Paraguay and Uruguay - and 9 from applying member Venezuela. Associate members - Bolivia, Chile, Colombia, Ecuador and Peru - may also hold seats on the Parliament, but with no voting powers. The Parliament was established in December 2006, but its first session of the Parliament was only held in May 2007.
"The creation of the Mercosur Parliament traces back to a 2002 process of establishing bodies and procedures aimed at the institutionalization and political autonomy of the bloc. During the XXVII Meeting of Mercosur Heads of State on December 17, 2004, at Ouro Preto, Minas Gerais, the CMC (Consejo del Mercado Común, Common Market Council) instructed the CPC (Comisión Parlamentaria Conjunta, Joint Parliamentary Commission) to write a protocol establishing the Mercosur Parliament, recommending its completion until the end of 2006. The CPC created the project in advance and on December 9, 2005, the Presidents of Argentina, Brazil, Paraguay and Uruguay signed the Constitutive Protocol of the Mercosur Parliament, creating the new body.
The first session of the Parliament should have been held before December 31, 2006, but it was only held on May 7, 2007, replacing the CPC. On June 2008, the MPs held their first parliamentary session outside the Mercosur headquarters in Montevideo, on the city of San Miguel de Tucumán, where the XXXV Meeting of Mercosur Heads of State was also being held".
Its flag is white with its emblem, forming by four blue stars of Southern Cross encircled by two leaves of a grey oval. Name of the Parliament is written under the logo. Spanish and Portugese variants are also used.
The logo of the Parliament contains the southern cross as in the Mercosul logo. I don't know when it was introduced, although using web search and the way back machine, you can find it being used in 2010.