We show that loss of synchronization of two identical coupled chaotic class B lasers can occur via a blowout bifurcation. This occurs when a transverse Lyapunov exponent governing the stability of a synchronized subspace passes through zero. A system of two laterally coupled lasers with modulated parameters is investigated numerically in a region of chaotic behavior. A total of five invariant subspaces are shown to exist. Evidence of a blowout from one of these subspaces is found in Lyapunov exponents and in the presence of on-off intermittency for small enough coupling strengths. At all parameter values investigated, the phases of the electric fields are shown to be precisely synchronized even though the amplitudes may fluctuate chaotically and independently. We discuss the implication that there will be bubbling effects in laser systems in the presence of noise and imperfections.