Well the Dubai Ports World issue would seem to imply otherwise. Dubai Ports World was trying to buy Us port management companies. After the executive branch approved it uproar caused congress/House Appropriations Committee to actually vote an amendment to block the deal. DPW eventually had to sell the US operations to an American group (they acquired the us companies through the purchase of a British company). The government wasn't sued over it. So it seems the government certainly can block purchases it doesn't like.