The 50-year-old actress - who is a former member of the controversial religion and now one of its biggest critics - told the organisation their ''days of getting away with it'' are coming to an end after the actor arrested over three allegations of sexual offences.
Leah shared a link to a news story about Masterson's charges and tweeted: ''Finally, victims are being heard when it comes to Scientology! Praise the lord! This is just the beginning Scientology, your days of getting away with it is coming to an end! #justice #scientologytheaftermath (sic)''
During the final season of her documentary series, 'Scientology and the Aftermath', the 'Second Act' star interviewed some of Masterson's accusers.
Crissie Bixler, whose interview was recorded in 2017, claimed the former 'That 70s Show' actor had attacked her in 2001 after they had been together for six years.
She alleged that she had blacked out after dinner and the next morning, she was in pain and felt as if she'd been poisoned.
When she asked her then-partner what had happened, he ''started laughing and said, 'I had sex with you.' ''
She added: ''I said, 'Was I unconscious?' and he said, 'Yes.' ''
Crissie told Leah she had joined the Church of Scientology when she began dating the 44-year-old actor and reported the incident to an ethics officer.
However, she claimed he told her the alleged attack wasn't rape ''if you've been in a consensual relationship.''
Masterson - who faces up to 45 years in jail if convicted - has insisted he is innocent and vowed to fight the charges.
His lawyer, Tom Mesereau, said in a statement: ''Mr. Masterson is innocent, and we're confident that he will be exonerated when all the evidence finally comes to light and witnesses have the opportunity to testify.
''Obviously, Mr. Masterson and his wife are in complete shock considering that these nearly 20-year old allegations are suddenly resulting in charges being filed, but they and their family are comforted knowing that ultimately the truth will come out.
''The people who know Mr. Masterson know his character and know the allegations to be false.''
The 'Ranch' actor has been accused of raping a 23-year-old woman some time in 2001, while the second charge relates to an alleged attack on a 28-year-old female in April 2003.
The third allegation dates between October and December 2003 and claims Masterson raped a 23-year-old woman at his Hollywood Hills home.
The District Attorney's office also announced they had decided against filing two other charges.
The biggest names in music royalty.