Strangely enough, Elizabeth Warren was able to put together comprehensive legislation to work towards ending Intuit's (to name the largest offender) corporate welfare [1] in the tax prep software space. Or is there an anti-private corporation/pro IRS tax prep lobbyist I'm missing?
I don't follow the sausagemaking process in DC, so I don't precisely know in that instance, but my guess would be a public advocacy group.
In my state legislature, which I follow, it's really common for various groups to write sample legislation. Everything from duck habitat preservation to open source software.
Congress cannot afford the lawyers needed to write that kind of legislation. The lobbyists write the laws they advocate for.