Washington (CNN) -- More than 100,000 Justice Department employees, including federal law enforcement officials from the FBI, ATF, DEA, U.S. Attorney offices and many other agencies, will know by Friday whether they will be required to work during a looming government shutdown.

U.S. Attorney General Eric Holder sent a memo to employees, obtained by CNN, that promised, "Should it become necessary to implement our contingency plans, you will receive notice from your manager no later than Friday April 8th regarding the designation of your position and status."

Justice Department officials have stressed repeatedly, but unofficially, that all employees involved in assuring public safety and protecting the nation against terror, espionage and crime threats will be considered "essential" employees and required to work during a layoff.

All FBI personnel will continue to work, and all 116 federal prisons will remain open, according to the department. In addition, criminal litigation will continue uninterrupted. But the department will be forced to stop or curtail activities including most civil litigation, community outreach to victims of crime and the processing of grants.

Holder told employees Wednesday that "as soon as funding lapses federal departments and agencies will not be permitted to incur further financial obligations performing activities funded by annual appropriations except those related to the orderly suspension of operations or performance of excepted activities."

As various federal agencies scramble to nail down funds with the shutdown looming, FBI Director Robert Mueller told Congress Wednesday the proposed short-term funding measure for the balance of this year would leave the FBI behind other agencies in dealing with vital intelligence.

Mueller testified the FBI needs the same assurance of full funding Congress is prepared to give the Defense Department.

"I can only say that under the proposed CR (continuing resolution) the FBI would be the only major partner in the intelligence community that is NOT fully funded. And while our intelligence community partners would be able to proceed with planned initiatives and programs, the Bureau (FBI) could not," Mueller said.

FBI and Justice officials declined to elaborate on Mueller's statements.

Mueller also insisted, "We simply cannot afford to return to the pre-9/11 days where hiring and staffing at the FBI was a roller-coaster that left most field offices understaffed." Mueller blamed pre-9/11 funding uncertainties for "degradation of the FBI's physical and information technology infrastructure that contributed to shortcomings in our capabilities."

Some FBI employees, like those in other law enforcement agencies, are nervously awaiting word on whether they will be declared "nonessential" and be subject to furlough.

Views on the matter varied. Unlike in 1995, this time few expect they will be paid for time they are furloughed, but as one employee told CNN, "I could use a little time off, paid or not." Another, however, complained, "Doesn't Congress understand we have bills to pay?"