In April, Hewitt threatened to sue the publication after it printed a story claiming that she was seeing an American trainer dubbed 'Minder Mark' behind husband Lleyton's back. However, Hewitt's mystery man was actually her brother Shaun Cartwright, while she demanded a public apology from the publication.
A statement released on the couple's official website states that legal proceedings were issued in the Supreme Court of South Australia early last month.
"In the proceedings issued on June 5, 2009 in the Supreme Court of South Australia, Bec seeks orders that New Idea disclose documents in its possession which will identify the source or sources for the story, including all photographs," the message reads.
"Whilst New Idea has twice proffered corrections and an apology for getting it wrong, they have, to date, refused to accept that the story carried defamatory imputations which were false or to disclose the identity of the source or sources behind the story.
"The purpose of the application to the Supreme Court is to find out precisely who those sources were and to understand how New Idea could have gotten it so badly wrong."