If you are talking about the diff lock I had a similar problem on my 2615HST. I couldn't get the pedal down with my full weight on it. From lack of use my diff lock linkage froze up (rusted). I had to soak all the linkage (mine went through the case from left to right side) with penetrating oil, Tap down on the pedal with a rubber mallet, lube again and pry up the pedal with a crowbar. I had to do this several times to get the lube into the linkage where it went through the case but eventually it freed up.
Not sure but I think your 3016 diff lock is like mine.
If your pedal does move freely the other thing I have seen on a friends tractor is the linkage stuck in the locked position and the owner busted a gear in one of the rear axle gear reduction housings because the axles were locked together when he made some sharp turns on a hard surface. Something had to give and it was the gears. Hopefully you don't have that problem.