Swedbank and Bursa Malaysia have both pledged support to the WWF's Earth Hour initiative, which will see lights around the world turned off for 60 minutes to raise awareness of climate change.
The event, which will take place at 8.30pm local time on Saturday, is styled by the WWF as a vote for the Earth against global warming.
Swedbank has pledged to cut out lights "as much as possible" at headquarters in Kiev, Stockholm, Riga, Vilnius and Tallinn. The bank has also called on its 9.9 million customers and 21 000 employees to turn off their lights for the hour.
Bursa Malaysia says it will cut all non-essential lights and air-conditioning in its offices for 60 minutes to support the cause.
Earth Hour began in Sydney in 2007, when 2.2 million homes and businesses switched off their lights for one hour. The following year 50 million people participated whilst global landmarks such as the Golden Gate Bridge in San Francisco, Rome's Colosseum and the Sydney Opera House stood in darkness.
This year the organisers say they hope to attract one billion participants and say 2140 cities, towns and municipalities in 82 countries have committed to the project.
The event is being used to put pressure on the world's leaders ahead of the Global Climate Change Conference being held in Copenhagen in December, where a successor agreement to the Kyoto Protocol will be discussed.