Shares of Netflix dropped more than 4 percent in midday trading Monday after Recode reported 21st Century Fox is adding more inventory to its FX+ streaming service.

The move spooked investors because it marks another step in big studios reclaiming their old shows from streaming competitors, pushing Netflix stock toward its worst day since November. While Netflix still carries FX's most popular show, "The People v. O.J. Simpson," Fox now has every season of its 31 original FX productions on FX+.

Confidence among Netflix investors also wobbled on August 9, when Disney announced it will remove its movies from Netflix to launch a direct-to-consumer service in 2019. Likewise, Fox's move now caters to paying TV customers — but only at an additional cost to the TV packages they have already bought.

CEO Bob Iger told CNBC in August that Disney had a "good relationship" with Netflix but decided to exercise an option to move its content off the platform. Movies to be removed include Disney as well as Pixar titles, according to Iger. Netflix said Disney movies will be available through the end of 2018 on its platform. Marvel TV shows will remain.

Fox did not say if or when it would remove its current offerings from Netflix.

Neither Netflix nor Fox were immediately available for comment.