An unemployed car salesman asked undercover federal agents to get plastic explosives and help him blow up an Internal Revenue Service building where thousands of people work, authorities said.

Charles Ray Polk, described as a militant tax protester, was charged Tuesday with planning to bomb the IRS Austin Service Center sometime this month."There's no doubt in our minds he had the intent to carry this out," said Mike Bradford, U.S. attorney for the Eastern District of Texas. "Polk has expressed very strong anti-government feelings, and specifically very strong feelings against the IRS."

Authorities were investigating whether another person was involved, he said.

Undercover agents contacted Polk in April after learning that he had bought 60 weapons through a straw man between October 1994 and April 1995, Bradford said. The transaction was illegal because the federal paperwork didn't name Polk as the owner, he said.

Polk then allegedly asked the agents for help in obtaining an illegal AK-47 machine gun. After they complied, he inquired about getting plastic explosives and asked the agents "for their participation in blowing up the building," Bradford said.

Polk planned to detonate the explosives at various locations to bring down the entire building, Bradford said.

"He was particularly interested in (targeting) enforcement agents of the IRS," Bradford said.

The center, which processes tax returns from four states, employs up to 4,200 workers.

Agents contend Polk planned the bombing between April 4 and July 28, when he was arrested for possessing the machine gun.

Bradford said the plot had no apparent link to the April 19 bombing of the Oklahoma City federal building, which killed 169 people and injured more than 500.

Polk, 45, has no criminal record. Bradford said he has some connection to anti-government militia groups, but the nature of the relationship wasn't clear.

NBC News reported that the IRS had tried to collect back taxes from Polk in recent years.

If convicted, Polk faces up to life in a federal prison and a $1 million fine. His trial is scheduled for Nov. 6 before U.S. District Judge William Wayne Justice.