SAO PAULO--AviancaTaca Holding SA (PFAVTA.BO) will join Star Alliance on Thursday, the head of the Colombian airline's Brazilian unit said Wednesday, meaning that newly formed airline Latam will likely be part of rival Oneworld alliance.

AviancaTaca, formed from the merger of carriers in Colombia and El Salvador, was invited last year to join Star Alliance, and the carrier is expected to officially disclose on Thursday that it will join the alliance, said Jose Efromovich, head of Avianca operations in Brazil.

Avianca's Brazil operations are kept separate from AviancaTaca, Mr. Efromovich said, but the Brazilian unit may decide to take part in Star Alliance as well starting next year.

Star Alliance, which also includes United Continental Holdings Inc. (UAL) and Deutsche Lufthansa AG (DLAKY, LHA.XE) as members, is expected to also disclose that Panama-based Copa Airlines will join the alliance.

AviancaTaca's decision also means that Latam, the Latin American airline formed by the takeover of Brazil's TAM SA (TAM, TAMM4.BR) by Chile's Lan Airlines SA (LFL, LAN.SM), won't be able to be part of the Star Alliance. This is because a ruling by Chilean antitrust judges said the merger could go through only if the two companies chose a single alliance, and added that the alliance couldn't be the same one in which AviancaTaca participates.

Lan currently belongs to Oneworld, while TAM belongs to Star Alliance, and now the expectation is that TAM will leave the alliance.

Write to Paulo Winterstein at paulo.winterstein@dowjones.com.