Former President Trump is expected to surrender in New York early next week, sources familiar with the matter told ABC News.

While a day has not been firmed up, sources said that Tuesday is the day being discussed by Trump's legal team and the Manhattan District Attorney's Office.

House Speaker Kevin McCarthy said in a tweet that the House GOP will use its power to hold Manhattan District Attorney Alvin Bragg "and his unprecedented abuse of power to account."

"The American people will not tolerate this injustice," McCarthy said, adding that Bragg has "weaponized our sacred system of justice against President Donald Trump."

House Republicans have requested documents and testimony from the Manhattan District Attorney's Office in its investigation of Trump, but Bragg has said he won't comply.

-ABC News' Lauren Peller

Manhattan District Attorney Alvin Bragg's office said in a statement that it has contacted former President Donald Trump's attorney "to coordinate his surrender" for arraignment on a state Supreme Court indictment, noting that it remains under seal.

"Guidance will be provided when the arraignment date is selected," the office said.

In the wake of the indictment, all officers with the New York Police Department have been ordered to show up in uniform Friday morning for deployments around New York City, police sources told ABC News.

There are no credible threats, according to the mayor's office.

A white powder was discovered in the mailroom at 80 Centre Street, where the Manhattan District Attorney has offices and where a grand jury has been meeting to hear evidence in former President Donald Trump's case, according to a court official. The powder was determined to be non-hazardous, officials said.

The powder came in an envelope addressed to "Alvin," an apparent reference to Manhattan District Attorney Alvin Bragg, according police sources.

Inside the envelope was a letter containing the typewritten message, “Alvin: I am going to kill you," with 13 exclamation points, according to sources.

This envelope followed a series of unfounded threats that targeted municipal offices in New York this week.

"For three days we got four emails," Susan Stetzer, district manager at Manhattan Community Board 3, told ABC News on Friday.

At least one of the messages prompted the court to pause a hearing in the New York Attorney General’s civil lawsuit against Trump.

None of the email messages mentioned Trump by name. One included what Stetzer described as a "horrible homophobic rant."

According to Stetzer, the messages came from @mail.ru domains and some contained Cyrillic characters. The FBI is aware but does not immediately assess that the emails came from Russia, according to a law enforcement official.

"We did not get one today so I’m hoping it stops," Stetzer said.

New York City courthouses will see increased security, the Office of Court Administration said Friday.