The merger between Spain's second and fourth largest telecom operators is the first major deal since the European Commission blocked CK Hutchison's $12.6 billion purchase of Telefónica's British mobile unit O2 in 2016.
This comes at a time when the Commission's head of Industry, Thierry Breton, is urging a rethink of the regulation of cross-border telecommunications agreements.
The EU competition watchdog said its preliminary investigation was ongoing. Orange declined to comment.
The Commission will open an in-depth investigation when it concludes its preliminary examination on April 3, according to the sources, who added that MasMovil is likely to have to offer solutions to get the green light.
The Commission, which acts as the guarantor of competition in the European Union, is also expected to reject a request from the Spanish antitrust body to take over the case.
Source: Foo Yun Chee, Reuters
