Carl Levin, Democratic senator from Michigan, is sponsoring a bill, S1346, to stop the abuse of offshore tax havens by US corporations. The bill was introduced in July of 2011. The details are here.
Here is a great detailed review from Citizens for Tax Justice. If you want to understand some of the accounting and legal tricks used to avoid US taxes, this document has plenty.
The bill would increase reporting requirements for offshore entities and treat tax entities managed by US companies as domestic corporations.
It also extends anti-money laundering reporting to off shore tax entities.
It would ban tax consultant contingent fees.
It also support the IRS process of issuing "John Doe" summons for tax information.
You can read the full bill summary here. S1346 Stop Tax Haven Abuse Act.
This bill has a snowballs chance in hell of passing.