The Mutant Liberation Front are now a confirmed part of 20th Century Fox's X-Men cinematic universe. The group were named as a terrorist group in Monday's episode of The Gifted on Fox.
The team came up when Coby Bell's Sentinel Service Agent Jace Turner was questioning his former colleague Reed Strucker (played by Stephen Moyer). Moyer was being interrogated by the Mutant Underground - the group he and his family come find refuge with when their children are found out to be mutants.
Turner compares the Mutant Underground to "terrorist" groups such as the Brotherhood of Mutants and the Mutant Liberation Front.
The Brotherhood were the key villains in the original 2000 X-Men movie, and have been mentioned in The Gifted's pilot episode as a still-active group.
The Mutant Liberation Front originated in comic books as the henchmen of Stryfe way back in New Mutants #86 by Louise Simonson and Rob Liefeld. Subsequent iterations have been led by Reignfire, Dani Moonstar, and Domino.
The Gifted airs Mondays on Fox.