White House officials have given further direction to federal agencies about the possibility of sequestration, and have told the agencies they “need to engage with their unions before taking any personnel action such as furloughs,”  the president of one of the largest unions for federal employees said Friday afternoon.

Colleen M. Kelley, president of the National Treasury Employees Union, said she was briefed by telephone Friday morning by officials with the Office of Management and Budget and the Office of Personnel Management.

“The officials said they expect to see some degree of variation across agencies and that some agencies may feel the need to take personnel actions sooner than others,” Kelley said in a statement. “OMB said it will continue to work with agencies to provide guidance so agencies make the best decisions possible.”

Kelley added that “agencies are being informed that should personnel actions become necessary they should be actively engaged with their unions and bargain impact and implementation consistent with the law and their collective bargaining agreements.”

The OMB and OPM officials told Kelley that “they are still hopeful that a deal can be reached” but are preparing for contingencies. Last-ditch talks are underway to try to avert going over the fiscal cliff

Regardless of whether an agreement is reached, “the operations of government will not change dramatically” Jan. 2, with officials “noting that there will be time to continue to finalize budget plans.”

Also on Friday, OPM posted answers to frequently asked questions about possible furloughs. The action follows the release of updated guidelines for federal agencies Thursday.