Activists from across the country are gearing up for the highly anticipated announcement of a grand jury's decision over whether a white police officer should face criminal charges in the fatal shooting of a black 18-year-old in Ferguson, Missouri, the Rev. Al Sharpton said Wednesday.

After months of heated protests over the death of Michael Brown, Sharpton called the situation in the St. Louis suburb "very tense."

Sharpton's National Action Network has plans in place for vigils and protests in at least two dozen cities no matter what decision is announced, he said. Demonstrators will gather outside U.S. government buildings to demand federal prosecutors take over the case.

"It is important that we have a fair and impartial proceeding," Sharpton said at a news conference at National Action Network headquarters in Harlem. "And it is clear that neither the family nor the community has confidence in the local prosecutor."

He added: "We are prepared to continue to mobilize. We are calling for everyone to act in a strategic, disciplined, non-violent way, but do not allow either decision to feel like the case is over."

There is no specific date for an announcement on whether Ferguson Police Officer Darren Wilson should face charges. The St. Louis County prosecutor has said he expects the grand jury to reach a decision in mid-to-late November.

The U.S. Justice Department is conducting a separate investigation, and it has not said when its work will be completed. It's looking into potential civil rights violations in Wilson's actions and the police department's overall practices, including whether officers used excessive force and engaged in discriminatory practices.

Sharpton said his group is on "high alert" over both the Brown case and the grand jury probe of the death of Eric Garner during an arrest in July on Staten Island. Evidence includes an amateur video a New York Police Department patrolmen wrapping his arm around the unarmed man's neck and medical examiner's finding that a chokehold contributed to the death.

Sharpton spent the bulk of the news conference responding to a report in The New York Times on Wednesday that there are more than $4.5 million in state and federal tax liens against him and his non-profit businesses. He called the front-page article misleading because it failed to emphasize that much of that figure stems from penalties and back taxes that are steadily being paid down as part of settlement with the Internal Revenue Services that was reported years ago.

"National Action Network and I owe no current taxes," he said. "We're talking about old taxes. We're not talking about anything new."