Hiding The Checkbook.
Much like the US House passed a bill to repeal the Affordable Care Act, basically a way to placate their "Tea Party" base. The Democrats in the US Senate may have tried much the same thing by trying to bring a watered-down version of the DISCLOSE Act to a vote. As they probably expected, and may have hoped, they could not break a Republican filibuster.
While the Republicans make this out to be a free speech issue. It could be yet another case of corporations having rights beyond that of a citizen. A corporation cannot be held criminally liable for its actions, and it seems that they have a greater right to anonymity than an ordinary person.
There could be another issue though. The Republicans are afraid of what would happen if people knew who was bankrolling them. One way I could see this law implemented is to have the donors on the groups web site. What would happen if someone saw that the CEO of the company that shut down the factory they work at was contributing to an ad? Or people saw that Wal-Mart and McDonalds were leading opposition to a State's effort to pass a Living Minimum Wage? One need only look to see what happened with ALEC to see what could happen if large donors were revealed.
I hope that the Democrats use this as an issue to rally their base, I also think more and more that the only way to limit the influence of corporations and their CEO's over the political process is the approach Move To Amend is taking.