A Vermont man has pleaded guilty after he was charged over spraying liquid cow manure on a US Customs and Border Protection vehicle. The man had confronted an agent about why he was not doing more to arrest undocumented people.

Mark Johnson, of Alburgh, pleaded guilty to simple assault on a law enforcement officer with bodily fluids and disorderly conduct on Tuesday (13 February).

Johnson, who does custom manure spreading, was first charged in August after covering a cruiser parked around 2 miles from the Canadian border.

The man first claimed he did not know that the agent was behind him while he sprayed the liquid manure.

However, he later said he questioned the agent as to why more was not being done to arrest illegal immigrants.

Johnson's guilty plea requires him to do 24 hours of community service in Grand Isle County and he had to write a letter of apology to the officer involved, the Associated Press (AP) reported. He is also not allowed to act in a violent or threatening behaviour or commit a crime.

MyChamplainValley.com reported that if Johnson follows his plea deal, his case will be dismissed and his records expunged. If not, he could face time in jail.

"My goal was to get him to accept responsibility and he did that today in court," Grand Isle County State's Attorney Doug DiSabito said. "I hope that Mr Johnson can keep his temper in check. It's behaviour we will not tolerate."