Me too, but just what parliamentay rules they are using are not described.
Took some diggin, but here it is (from http://www.gunowners.org/a030204a.htm):
How to Push a Clean Bill Through the Senate (101)
Gun Owners of America
8001 Forbes Place, Suite 102
Springfield, VA 22151
(703)321-8585
How could Majority Leader Bill Frist (R-TN) have brought the gun maker protection act (S. 1805) to the floor of the U.S. Senate without opening it up to several anti-gun amendments?
The answer lies in using a parliamentary maneuver commonly known as "treeing the bill" or "filling out the amendment tree."
Normally, Senate rules allow first and second degree amendments to be considered after a bill hits the floor for consideration. It is at this time that anti-gun senators can add a litany of gun restrictions by offering them as amendments to legislation.
However, the Senate Majority Leader can preclude all of this by closing off the available amendment "slots" before the Senate considers the bill. He can do this without getting Unanimous Consent from other senators, as he has the right to be recognized before any other senator -- even repeatedly recognized.
The following is an example of what Senator Frist could have done:
(1) Frist should have offered a first-degree perfecting amendment -- preferably setting the effective date of the bill one day after its enactment. At this point, he would have asked for the "yeas and nays."
(2) Then Frist should have offered a second-degree amendment supplanting the one day effective date with a two days effective date.
(3) Then Frist should have moved to recommit the bill with instructions that it be reported back forthwith with an amendment setting the effective date one day after enactment.
(4) Then Frist should have offered a first-degree amendment to the instructions replacing "one day" with "two days" and, after getting the "yeas and nays," a second degree amendment replacing "two days" with "three days."
(5) Then Frist should have filed cloture -- that is, moved to shut off debate -- on the bill.
At this point the bill would have been TOTALLY UNAMENDABLE! Senators would have been forced to vote "up or down" on S. 1805. No other amendments would have been in order.
There would have been no Feinstein semi-auto ban amendment. No McCain gun show ban. No Lock Up Your Safety restrictions.
Senators would have been forced to choose between voting for the trial lawyers (who are terrorizing the gun industry with frivolous lawsuits) or voting to protect the Second Amendment.
Unfortunately, Senator Frist chose the politically risky gamble of trying to win close votes on the floor of the Senate (on issues such as semi-auto bans and gun show restrictions), when he simply could have "bullied" the bill through the chamber in an unamendable form.