Coca-Cola and PepsiCo have both signed voluntary global guidelines on land tenure.
The guidelines are designed to safeguard local people's rights to land and food in the face of large-scale land acquisitions in developing nations.
Oxfam New Zealand said an area of land the size of Auckland is being sold to foreign investors for farming every four days in poor countries.
While the land was sold as unused or undeveloped, Oxfam said poor families were often living there and growing food.
PepsiCo signed this week and also pledged to carry out social and environmental assessments across its global supply chains, beginning in Brazil, its top sugar-sourcing country.
Coca-Cola signed in November.
