I would argue they don't have much of a choice:
"The economic sanctions put in place as a result of the invasion and the
increasingly uncertain security situation make it impossible for Cogent
to continue to provide you with service."
I would expect to see others follow suit if that is the case.
That's an interesting slope to slide along...
I fully understand ISPs disconnecting customers for non-payment; we've
all had to do that at one point or another in our careers, I'm sure.
However, that's generally done *after* the customer has demonstrated
an inability or unwillingness to pay their bills.
This doesn't seem to indicate that any existing invoices have gone
unpaid past their due date, but simply that there is *concern* that a
future bill might go unpaid due to the economic sanctions.