The European Commission resumed its investigation into the case on March 18 after a two-week stoppage while waiting for data from the companies, a filing on its site showed.

The EU competition watchdog is looking into the impact of the deal in Italy and Britain and at whether rivals can compete with the companies, according to a questionnaire sent to independent opticians seen by Reuters.

EssilorLuxottica's eyewear and retail brands include Oakley, Sunglass Hut and Spectacle Hut while GrandVision's chains include Vision Express in Britain and For Eyes in the United States.

(Reporting by Foo Yun Chee; editing by Jason Neely)