A US Supreme Court ruling has thrown doubt on two high profile corporate fraud prosecutions, that of former Enron chief executive Jeffrey Skilling and ex-media baron Conrad Black, and may make it harder for the US government to bring cases against corporations and senior executives in the wake of the financial crisis.

Justice Ruth Bader Ginsburg's ruling limited the reach of a federal fraud law used in cases of alleged public corruption by government officials and fraudulent activity by business executives, according to Reuters.

The judge said the fraud law at issue only covered bribery and kickbacks, and that Skilling's alleged misconduct did not involve a bribe or kickback. The case involves a 28-word law adopted in 1988 that makes it illegal for public officials and executives to commit fraud by depriving those they work for of the right to 'honest services'.

Skilling's lawyers argue he did not breach his 'honest services' duty because he never was dishonest to his employer, he always acted in Enron's interest and prosecutors never showed he personally benefited from his allegedly fraudulent acts.

The court also ruled that the convictions of Black and two former colleagues for defrauding shareholders of former newspaper publisher Hollinger International must be reviewed because of mistakes in instructions to the jury instructions about the fraud law.

The court did not overturn the convictions, and both men will remain in prison while the cases are heard again in lower courts. Ginsburg said in Black's case, the lower courts must determine if the jury instruction error was harmless, while in Skilling's case, she said the conspiracy and fraud conviction was flawed, but may not have to be reversed.

The US justice department has said it would defend the Skilling and Black cases in the lower courts. The two men have been convicted on other charges besides fraud, and the ruling ensures further legal proceedings to determine the fate of their convictions on all the charges.