As immigrants and their supporters prepared for a massive boycott on Monday, opponents of illegal immigration went to work building a border fence meant to symbolize their support of a secure border.

About 200 volunteers organized by the Minuteman Civil Defense Corps of California began building a 6-foot barbed wire fence Saturday along a quarter-mile stretch of rugged terrain in Boulevard, about 50 miles east of San Diego.

Tim Donnelly, the group's leader, said volunteers ate apple pie and hot dogs as they worked on the fence, which was connected to an existing 12-foot-high fence previously built by the federal government.

The volunteers wanted to send a message to Congress that the government should block entry to the United States and not grant amnesty to illegal immigrants, Donnelly said.

Thousands of immigrants and their supporters are expected to boycott work and schools Monday to raise awareness of their contributions to society.

"This was largely sent as a message to Congress so they'll see on May 1, there are jobs that even illegal immigrants don't want to do, but Americans are more than willing to do them," Donnelly said, referring to the fence-building.

Donnelly said before the event he called a local contact at the U.S. Border Patrol and told him what the volunteers planned to do. He declined to name the local contact.

Department of Homeland Security spokesman Richard Kite said Saturday there had been "no indications our operations or the property of the Border Patrol have been tampered with or altered in any way by citizen groups."