Right. We accept that corporations lobby constantly. Why shouldn't their employees have a voice, too?
Anyone should be able to lobby.
There's nothing overtly nefarious about lobbying.
Lobbying is 'telling government about something specific'. Usually in your own interests, but the interests of the people should interest the government.
The problem is the asymmetry of power and access.
Seems reasonable to me for unions to be involved in lobbying.