Even if the laser doesn't cause temporary or permanent injury to the pilots' eyes, it causes them to lose night vision.
The most well-known cause of this is the pupils of your eyes. In the dark, the pupils open up to allow in as much light as possible. When they're exposed to a sudden bright light, they close up again. If the bright light goes away, it takes your eyes some amount of time (say, a minute or two) for your pupils to open again. During that time, you can't see very well at all. Not good, if you're trying to land a plane. You can experience this for yourself by playing around with the lights indoors at night: if you turn the lights off, you can see very little but, gradually, you begin to make things out as your pupils open. If you then turn the light back on, it feels uncomfortably bright until you get used to it again.
Less well-known is a chemical called rhodopsin, in the rod cells in your retina. Rhodopsin is extremely sensitive to light (even to single photons), and light makes it change shape. Other proteins bind to this new shape and a few little chemical reactions result in an amplified signal being sent to your brain. Most of your vision in the dark comes from the rod cells because of their high sensitivity; the other cells (the cones) require tens to hundreds of photons to fire so they're great for colour vision in decent light but not much use in the dark.
However, being bound to other proteins means that the rhodopsin in your eyes is "used up" as light comes into your eyes. When its dark, this happens slowly enough that the rhodopsin can be regenerated but a sudden burst of bright light, such as from a laser, consumes all the rhodopsin in your eyes almost immediately. Now, you're only seeing with the cones, and you're not seeing much. The really bad news is that it takes at least 5–10 minutes for a decent amount of rhodopsin to regenerate and 30–45 minutes to get back to the full amount. So now, your pilots are operating on quite seriously decreased vision for a substantial amount of time.