Under the rule to be formally published Wednesday, anyone who buys large amounts of ammonium nitrate, including farmers or workers seeking to use it as an explosive in mining or construction, would be required to register in advance. If they're not on any government watch lists, they'd get a federal user number which, along with a photo ID, would allow them to make purchases.
Dealers would be barred from selling more than 25 pounds of ammonium nitrate to anyone who wasn't registered and would also be required to keep records of all sales. They would also have to report losses or thefts within 24 hours.
Ammonium nitrate, mixed with diesel fuel, was the principal ingredient in the truck bomb that Timothy McVeigh detonated outside the Oklahoma City federal building in 1995. It was a favorite of the IRA's terror campaign in London in the early 1980's. And it was used in the bombings of the U.S. embassies in Africa in 1998, in a series of bomb attacks in Turkey in 2003, and in last month's bombing of government buildings in Oslo, Norway.
Shortly after the Oklahoma City bombing, the federal government sought the voluntary cooperation of dealers to ask anyone buying large quantities why they wanted it. It encouraged dealers to report suspicious activities or thefts.
But as the federal government has moved to regulate sales, ammonium nitrate has become harder to find, and its price has risen.
"It's much harder to find now, because retailers have said they're not going to stock it and have to go through all the trouble of keeping records," said Tyler Wegmeyer of the American Farm Bureau Federation, which has supported the federal regulatory efforts.
"It used to be the cheapest fertilizer, but it isn't anymore," he said.