U.S. lawmakers have received an emergency security plan in anticipation of potential violence in Washington when a joint session of Congress meets Wednesday to count Electoral College votes to affirm Joe Biden’s victory, according to sources.

The urgent precautions were handed out Monday in the House and Senate and include guidance for legislators and staff on using underground tunnels while moving between chambers in the Capitol and to nearby office buildings throughout the day, according to a person familiar with the plans.

The security measures also provide emergency phone numbers for Capitol police and House and Senate sergeants-at-arms to report any incidents or issues.

Further, the guidelines encourage lawmakers to arrive at the Capitol early, make use of garages with barricades and security access points, the source said, according to Bloomberg News.

Lawmakers were also briefed on extensive road closures around the Capitol and elsewhere in Washington.

In recent days on social media, President Donald Trump has summoned protesters to the nation’s capital to help pressure lawmakers to reject the Electoral College vote in the hopes of overturning the results and hand another term to the incumbent.

“See you in Washington, DC, on January 6th. Don’t miss it,” Trump tweeted Sunday, apparently hoping for a big turnout of people supporting his unproven claim that voter fraud was behind his defeat by Biden.

Washington, D.C., Mayor Muriel Bowser urged residents not to engage with any protesters “seeking confrontation,” and some downtown businesses have already boarded up windows in case there is violence.

So-called First Amendment demonstrations are permitted by the National Park Service, but officials are preparing for potential unrest.

Bowser has asked city residents not to come downtown or to the Capitol area on Tuesday and Wednesday. Under her direction, the city’s Homeland Security and Emergency Management Agency on Monday activated the district’s Emergency Operations Center, to coordinate federal and local responses to the demonstrations.

“We will do what we must to ensure all who attend remain peaceful,” Bowser said in a Sunday statement.

Pro-Trump protests in November and December in Washington and some other cities ended in violence and property damage. Some far-right protest groups, such as the Proud Boys, have said they will show up for the demonstrations this week.

On Tuesday, the Metropolitan Police Department begins its full activation for responses through Wednesday. Washington starting on Tuesday will ban street parking along some avenues.

On Monday morning, workers were seen outside some downtown businesses boarding up windows and doors.

Information provided by Tribune News Service was used to supplement this report.