Guatemalan legislators approved a new law Tuesday that tightens adoptions, while allowing pending cases — mostly involving U.S. couples — to go through without meeting stricter requirements.

The new law will enable Guatemala to comply with the Hague Convention, an international agreement designed to protect adopted children from human trafficking. The Central American country sent 4,135 children to the U.S. last year, making it the largest source of babies for American families after China.