Is a visa required when working remotely?

I realize this might be case by case but I frequently see international companies listing a remote working option. If they are based in a different country from my citizenship, should I assume that a work visa is required to work for them? Sometimes the job mentions a contract working option. Is that considered a work-around to requiring a work visa?

I will try to google this a little but don't see something clear in the initial results. Thanks.