Thousands of activists from across the country are expected to descend on the Virginia State Capitol on Monday to rally against sweeping new gun control proposals supported by state Democrats.

But the rally in Richmond — billed as a peaceful event to lobby lawmakers to defend Second Amendment rights — has quickly set off fears of potential violence and chaos. Discussions about the rally have been lighting up online platforms frequented by anti-government militia groups and white supremacists for weeks, and various extremist groups have vowed to attend.

Tensions escalated this week when Gov. Ralph Northam declared a state of emergency and temporarily banned weapons on Capitol grounds, citing credible “threats of violence.” The F.B.I. also announced the arrest of three suspected neo-Nazis who the authorities said had obtained weapons and discussed participating in the Richmond event, intensifying concerns.

Here’s what you need to know about the rally and what to expect for Monday.

Why is the rally happening now?

Virginia Democrats flipped the state House and Senate in November, wresting the General Assembly from Republican control in a state that was once the seat of the Confederacy.