Since Citizens United opened the floodgates of corporate money into elections, it is in shareholders' interests to know how those dollars are spent.
Political donations can cost extremely large sums and impact a company's reputation, and shareholders have a right to know how this capital is being spent. Even worse, with no oversight corporate managers are free to try and influence government policy in ways that serve their own interests over the shareholders. There is already evidence that this is going on.
There is a petition by 10 legal scholars with the Securities and Exchange Commission that says this already, 4-637 from Aug. 3, 2011. The administration should pressure the SEC to adopt this rule as soon as possible.
More info in this NYT editorial: http://nyti.ms/16KrkFU