matgopack misses one very crucial difference. A guild is run by owners of the businesses, the shops, factories, tanyards, etc. A labor union is composed of people who work at the shops, factories, tanyards, etc.

The guilds were a cooperative effort by owners to restrict competition, to keep, say, 20 cutlers from working in a town that had enough trade for 5. They demanded qualifications for the workers in those businesses: on the face of it, to keep up the quality of the goods made, but in practice to allow the favored apprentices and workers to advance in the trade and the un-favored to stay put. Fairness to workers was not the priority. To gain entry into the guild of watch makers in Geneva in the 18th., for example, an apprentice's family had to pay a master for an apprenticeship, as well as bonding their son for several years as an unpaid worker. The guilds made it impossible for someone to set up a business without first having the permission of the guild.They also were social organizations: guilds had banquets, ceremonial meetings, kept records. (Some guilds, like the Long String Bow Makers in England, had ceased to be anything but a social fraternal organization by the 18th c.) If guilds resemble anything, perhaps it's the late 19th c. business "trusts" who managed to keep tariffs high and cooperatively set prices.

A craft union in some ways also wants to restrict the market; it wants to set wage and working conditions requirements for the businesses that employ its members. But it doesn't include the businesses as members.

First off, a bit of nomenclature - the AFL is not an industrial or post-industrial union, it's a craft union. The CIO and the IWW were industrial unions. The difference? The AFL organized along trades, so (using an example of an auto factory), each step in the process would have a different union - painting, electrician, etc. A classic example of a craft union would be plumbers. Industrial unions instead bring all the workers in a single industry into a single union - that's the innovation that brought about unions like the UAW. Now, obviously that evolved (the AFL would reform to try to be more along industrial lines, and the CIO would merge back with it). I assume you meant industrial era, but I wanted to throw that in there.

Medieval/early modern guilds were often hereditary, and tended to be organized along masters/journeymen/apprentices. They had legal rights/privileges, that excluded non-guild craftsmen from playing a role.

That made them very different from industrial unions like the CIO or the IWW, that seeked to organize unskilled labor along industrial lines. In comparison, craft unionism is very much in line with the idea of a guild - where skilled tradesmen organize, and have control (through apprenticeships) of who can join and practice. Medieval/early modern guilds just had more defined, legal/traditional roles - whereas craft unions had to rely more on their skills and solidarity, without legal limits and privileges.