Is it okay to use a butcher block that has been covered with polyurethane?

I wouldn’t use it. Butcher block should be treated only with food-safe oils.

The point of a butchers block is to protect both the work surface and knife from damage. Unfortunately wood is porous and this can be a problem if you are chopping raw meat on the block as it will soak up all the blood and what have you and then transfer it on to everything else that you put on it. This is bad therefore you need to fill all those pores in the wood with something else. If I was going to prep a new virgin block then I’d use mineral oil.

If the surface is not going to be used to chop on then polyurethane is acceptable and perfectly food safe so it is not unusual to find it used to protect the surface particularly as it’s much lower maintenance than oil. When you oil the block you need to keep doing every so often. If you’re going to use the block to chop stuff up then I would avoid it.

I concur. Butcher blocks should not be used for meat in general unless you are prepared for a lot of maintenance. However, for stuff like baking then it’s perfectly fine. Just don’t get too crazy on it with a sharp knife.

I wouldn’t use it for cutting. Polyurethane is a petroleum-based substance and therefore toxic. I have a butcher block that I oil with plain mineral oil I get at the pharmacy.

Wood is safe for cutting boards and so is dried polyurethane.

…those using wooden cutting boards in their home kitchens were less than half as likely as average to contract salmonellosis…those using synthetic (plastic or glass) cutting boards were about twice as likely as average to contract salmonellosis…we regard it as the best epidemiological evidence available to date that wooden cutting boards are not a hazard to human health, but plastic cutting boards may be.
http://faculty.vetmed.ucdavis.edu/faculty/docliver/Research/cuttingboard.htm

The Folly of Food-Safe Finishes
Despite what you’ve read elsewhere, almost every wood finish should be considered food-safe…
http://www.popularwoodworking.com/features/finish3.html

I wouldn’t. What kind of moron puts polyurethane on a butcher block?

Our butcher block counter is merely aesthetic. We still use cutting boards and plates, but it looks very nice.

You could always buy it and sand off the polyurethane.
@jaytkay I don’t care what Bob Flexner says. Ingesting bits of polyurethane can’t be good for you. (My guess is he votes republican…)
I treat my 12 butcher block tables with a beeswax finish. This provides a barrier for liquids which just mineral oil does not.
This has some good info about refinishing.