OTTAWA -- Two high-profile American senators are demanding tougher action against a Canadian aerospace company that has admitted to exporting military software to China in violation of U.S. law.

Pratt and Whitney Canada, owned by U.S. defence giant United Technologies Corporation, has acknowledged selling the computer programs that could allow China to complete the development of its first modern attack helicopter.

U.S. senators John McCain and Carl Levin, who sit on the Senate Armed Services Committee, want the Obama administration to go beyond the US $75 million fine imposed on Pratt and Whitney and another subsidiary, Hamilton Sundstrand.

In a letter to both Defence Secretary Leon Panetta and Secretary of State Hillary Clinton, the two senators demanded the Pentagon consider suspending or blocking Pratt and Whitney Canada, based in Longueuil, Que., from participating in U.S. defence contracts.

They say they're concerned that the violations "may have caused significant harm to our national security."

Both senators are also calling for company officials to be held personally accountable for what they describe as "criminal misconduct."