The Supreme Court's conservative bloc sounded poised Wednesday to strike down on free-speech grounds a 102-year-old ban against corporations spending large amounts of money to elect or defeat congressional and presidential candidates.

If the justices were to issue such a ruling in the next few months, it could reshape American politics, beginning with the congressional campaign in 2010. Big companies and industries -- and possibly unions as well -- could fund campaign ads to support or defeat members of Congress.

For example, the health insurance industry would have a much greater ability to target for defeat lawmakers who supported a so-called public option for medical insurance. Banks and investment firms could oppose representatives who favored stricter regulation of the financial industry.

And far more money could flow into elections. Last year, the political parties spent about $1.5 billion on campaigns, while corporations earned more than $600 billion in profits.

Since 1907, federal law has prohibited corporations from giving money to candidates. And since 1947, corporations and unions have been barred from spending money on their own to urge voters to elect or defeat federal candidates.

Of course, corporate executives, as individuals, can contribute money to a corporate political action committee, or PAC, but these amounts are modest compared with the funds available to corporate treasuries.