There was some discussion of that in this thread.
They brought up a verification from Inventables that their lino (from Speedball) was laser safe. And then, there were some rule of thumb guidelines re: color and backing material.
I bought the same Speedball sheet @Joe linked to above, from Amazon, and it passes those informal tests.
That’s all still basically unverified, but things could be a lot sketchier. (I’m relatively sure Speedball will report back that we’re fine.)