Sirius and XM have disclosed in SEC filings that they've filed the required Hart-Scott-Rodino "Notification and Report Form" effective on March 13th.

The filing essentially just describes the proposed transaction for the FTC and DOJ. Now we have a 30-day waiting period that allows regulators to request further information in order to help them assess whether the proposed transaction violates the antitrust laws.

Read more about the Hart-Scott-Rodino Antitrust Improvements Act of 1976 here.