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.
