The drinks company has upset pro-Palestinian activists for maintaining a large factory in an Israeli settlement in the West Bank - a territory captured by Israel in 1967.
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They feel trade from such settlements is illegal and denies Palestinian rights, a view which is shared by humanitarian group Oxfam.
"Scarlett Johansson has respectfully decided to end her ambassador role with Oxfam after eight years," read a statement released by the star's management.
"She and Oxfam have a fundamental difference of opinion in regards to the boycott, divestment and sanctions movement. She is very proud of her accomplishments and fundraising efforts during her tenure with Oxfam."
Earlier this month, Scarlett became SodaStream's first global brand ambassador. She will feature in an advert which will be played during the Superbowl on 2 February. Last week in response to negative comments about her new appointment, the 29-year-old said she was a "supporter of economic cooperation and social interaction between a democratic Israel and Palestine."
In response, Oxfam said they were "considering the implications of her new statement and what it means for Ms Johansson's role as an Oxfam global ambassador".
Since starting work for the organisation in 2007, Scarlett has travelled to Sri Lanka, India, and Kenya to raise awareness of the impact of poverty and traumatic disasters. A spokesperson from the organisation said: "Oxfam has accepted Scarlett Johansson’s decision to step down after eight years as a Global Ambassador and we are grateful for her many contributions.
"While Oxfam respects the independence of our ambassadors, Ms Johansson’s role promoting the company SodaStream is incompatible with her role as an Oxfam Global Ambassador.
"Oxfam believes that businesses, such as SodaStream, that operate in settlements further the ongoing poverty and denial of rights of the Palestinian communities that we work to support. Oxfam is opposed to all trade from Israeli settlements, which are illegal under international law.
"Ms Johansson has worked with Oxfam since 2005 and in 2007 became a Global Ambassador, helping to highlight the impact of natural disasters and raise funds to save lives and fight poverty."