The saga of the "mobile machinery exemption" continues. The Internal Revenue Service proposed last June to end a 57-year-old exception that has kept mobile cranes, concrete pumpers, drilling, logging and mining equipment free of federal excise taxes. If the IRS issues a final rule to end the exemption, the chassis of such equipment would be subject to the new-vehicle tax. In addition, existing as well as new equipment would be subject to the federal fuel, tire and heavy-vehicle use taxes. And states that follow federal exemptions might start applying their taxes and registration fees as well. By the December 4 filing deadline for comments, the IRS had received more than 300 letters opposing the change, including one signed by 80 members of Congress. Next step: an IRS hearing on February 27, which promises to draw a lot of speakers.