No. They can refuse it.
However, the logic behind it is very questionable.
Example:
An American Airlines 767 captain with 10,000 flying hours on type, with an FAA Class One is allowed to fly his plane to Heathrow, despite his eyesight being outside of JAA initial AND renewal requirements.
He can continue to do this as long as he is flying an N-reg 767.
However, if overnight, the aircraft's reg was changed to a G-reg.
He would not be able to fly the aircraft back to the US.
Does that make sense??