Europe's top court has ruled against the British government's golden share in airport firm BAA and a Spanish law granting state control over privatised firms.
European Union treaty rules allow governments to keep a grip on private firms to protect services vital to the general interest.
But the European Court of Justice ruled the arrangements in place were not justified by the interest protected and restricted the free movement of capital.
"Both the Spanish and UK rules entail restrictions on the movement of capital between member states," the European Court of Justice said.
The ruling has boosted the EU Commission's crusade against investment hurdles.
The Commission, the executive of the 15-nation EU, recently challenged golden share arrangements in Italy, Spain, Germany, Denmark and The Netherlands in a bid to free up cross-border investment and raise the bloc's competitiveness.