An order would likely impact dozens of firms including JPMorgan Chase, Exxon Mobil, General Electric, and Koch Industries. All hold government contracts.
In 2011, following a Dark Money infusion into the 2010 midterms, the administration suggested a similar executive order, but backed down against pressure from lobbyists.
This is the presidents most effective direct action to push back against the "Citizens United" decision.
If you wont make this an executive order then tell the american people why you wont. America deserves action to preserve their right to fair elections.