07/17/2013 at 11:00 AM EDT
Leam Remini is known for being outspoken (after all, she is Brooklyn-born) but she took gutsiness to a new level last week when it was announced July 11 that she was leaving Scientology
, the church where she's been a very visible member for more than three decades.
"I wish to share my sincere and heartfelt appreciation for the overwhelming positive response I have received from the media, my colleagues and fans," Remini, 43, said in a carefully worded statement
the next day.
What Remini didn't say was that she'd tangled with the Church
, and questioned its leader David Miscavige. As a result, according to several sources close to the actress, she was required to go through extensive "security checks," a practice of intensive personal questioning.
The church says it won't comment on Remini or any member in detail and maintains that critics misunderstand the nature of security checks.
"Leah is saying 'I'm seeing things are wrong,' " says her sister Nicole Remini-Wiskow, who also left the church in 2005. "She fights for what she believes in."
Although Remini has remained silent since her statement and is now, according to her sister, "laying low," friends say she is not afraid of what's ahead. "Stepping away from Scientology will be challenging," says one insider. "But she will fight."
For exclusive details on Leah Remini's decision to leave Scientology, pick up the new issue of PEOPLE, on newsstands Friday.