Germany would expect Internet companies "to tell us in Europe who they are giving data to," she said in an interview Sunday with Germany's public broadcasting network.
She made the comments following revelations a U.S. government program collected user data from Internet companies and reports the program also eavesdropped on European Union and German officials.
"I expect a clear commitment from the United States government that in future they will stick to German law," Merkel said.
She is facing calls to reveal how much her government knew about the activities of the U.S. National Security Agency, the BBC reported.
A patchwork of laws across the European Union hampered efforts to determine and control who has access to Internet users' data, she said.
"We have a great data protection law [in Germany.] But if Facebook is registered in Ireland, then Irish law is valid, and therefore we need unified European rules," Merkel said.
Germany would take a "very strict position" in discussions on data rules that would apply across the European Union, she said.