Fifita was issued with a breach notice last week by the NRL.
"It has been decided to impose a fine of $20,000," an NRL spokesman said on Thursday. "Our competition cannot be used as a platform to promote inappropriate causes such as this."
Fifita was the subject of a lengthy NRL integrity unit investigation over his relationship with Loveridge, a childhood friend from western Sydney. Loveridge was sentenced to 10 years' jail for the unprovoked, drunken one-punch killing of Thomas Kelly in Kings Cross, in 2012.
As a result of his stand, Fifita was snubbed for the Clive Churchill Medal, despite inspiring Cronulla's historic NRL premiership triumph.
And he was not considered for the end of year Four Nations, after NRL chief executive Todd Greenberg said Fifita had "failed to live up to standards set by the [Kangaroos] side".
The NSW Origin prop threatened to walk out on the code and join rugby union, after the Four Nations snub.