Rep.Don Beyer is doubling down on his plans to block the construction of President Trump‘s massive arch with some old-fashioned civil disobedience … sleeping bag, handcuffs and all.

The Virginia congressman joined “TMZ Live” Friday … insisting his protest plans are no publicity stunt, even after a federal judge temporarily blocked construction for 14 days.

The proposed 250-foot arch would tower over Memorial Circle, just outside Arlington National Cemetery … drawing backlash from critics who say the massive structure would overshadow the sacred burial ground and disrupt historic views.

Beyer says if there’s any sign Trump plans to move forward, he’ll rush down the site … along with plenty of supporters ready to keep watch 24/7. He even warned they can’t let their guard down after dark, saying Trump’s administration has shown it can do “evil things in the middle of the night.”

And he insists the protest can make a real difference … pointing to civil rights leaders John Lewis and Martin Luther King Jr. as proof civil disobedience can bring change.

As TMZ previously reported … Beyer told us he’s willing to get hauled off in handcuffs to stop the project, taking a page out of Jane Fonda‘s protest playbook.

Beyer even invited the actress to join him.

The fight is personal for Beyer … his parents, grandparents and sister are buried at Arlington, and he says the cemetery is no place for a monument to Trump’s ego.