Tacky in two ways - 1) inviting people to a shower when they aren't invited to the wedding/reception and 2) someone is trying to make money off the shower. Either of those reasons would prevent my attending.
However, it seems like many here on e-hell think it's okay to invite co-workers to wedding showers regardless of the fact they aren't being invited to the wedding. I just don't get the reason for that exception. Yes, many people cannot afford or are otherwise unable to invite everyone they work with to their wedding and that's perfectly okay. I think most coworkers are understanding. But then, those same excluded coworkers shouldn't be expected to finance the happy couple's lifestyle via shower gifts. It just screams "greed" and I truely don't get it. It's like trying to get something for nothing I guess.
I don't think you can invite coworkers to your shower but work can throw you a shower ie every employee who gets married gets a work shower by virtue of working there.
I've never been invited to a work bridal shower for someone to whose wedding I wasn't invited. In fact, where I work, they've never had a work bridal shower at all. Because no one here invites everyone from work to the wedding. It's just too big of a work environment.
One time, there was a sort of pre-wedding party for someone who was getting married. She was someone who had been working here for years and she knew everyone and everyone knew her. One of her close friends at work really wanted to give her a party with all the females. The bride graciously accepted the party but it was made explicitly clear that this was absolutely not a shower, that no gifts were to be given and that it would be fully hosted by the friends. We went to a wine bar and had drinks and munchies and it was really nice. But since she wasn't inviting most of us to the wedding (which was fine and perfectly understandable) it was the right thing to do -- party to celebrate her upcoming nuptials but no gifts.
Now, on the other hand, baby showers are quite common here. All the females get invited even though it's usually just the ones who really know or work with the mother-to-be who show up.