You need to research any law in DC on condo associations. The association should probably hire an attorney to get a written legal opinion. I doubt anyone here has that specialized knowledge.
The association probably can put a lien on the condo, so at least the fees up to that point would have to be paid if it is sold.
However, if a condo owner does not pay the fee, I would say it is completely reasonable to withhold any service that fee covers. Of course, you can't mess with the mail and things like that.
Many condo fees include things like basic cable tv, which could be cut off.
The condo association should probably have such powers already in the bylaws or district code.

