When he signed on for the role of Nick Fury, Samuel L. Jackson's contract was for a whopping nine films in the Marvel Cinematic Universe. At the time it seemed a ridiculously long deal.
Cut to only a few years later, and two-thirds of that deal is already done (his "Marvel's Agents of SHIELD" cameo doesn't count). Jackson spoke about the looming deadline ahead for him and the studio:
"I just know that the Marvel Universe is there, that there are things going on, and that I have three pictures left on my nine-picture deal. That's all I know. I've done six [Marvel movies], and I'm about to do [number] seven, so I'm running out of Marvel pictures -- unless they extend my contract."
The seventh in question is "Avengers: Age of Ultron" which begins filming in March. This also means appearances from Fury outside "The Avengers" and "Captain America" in the near-future are looking less and less likely.
Would he sign up for more though? Jackson responded: "Why wouldn't I?". The real question though is if the notoriously frugal Marvel would still want him.
Source: Heat Vision