Pharmaceutical giant Pfizer is offering early retirement to U.S. workers ahead of layoffs early next year, it announced internally to employees.

The company, which currently employs more than 90,000, didn't say how many people it plans to cut. But it told employees Tuesday that all business units and divisions will likely lay off nonunion workers, according to materials outlining the workforce reduction program obtained by CNBC.

"As we prepare for growth we are creating a simpler more efficient structure which will affect some managerial roles and responsibilities. We are offering enhancements to certain benefits to lessen this effect," Pfizer spokeswoman Sally Beatty said in an email. Overall, its workforce will shrink by "a couple percentage points," she said.

Incoming CEO Albert Bourla, who's succeeding Ian Read on Jan. 1, shuffled the company's senior management team last week and is leading the efforts to restructure the pharmaceutical giant into a more nimble company. Pfizer announced plans in July to reorganize into three units, separating its consumer health-care business that it had been trying to sell.

The head count reduction plan is part of its restructuring, the company told employees in an email obtained by CNBC. "To achieve our full potential we will need to create a simpler and more efficient organization," it said.

"As we simplify the organization to avoid duplication, create single points of accountability and reduce the number of layers within teams, there will be an impact to some managerial roles and responsibilities across the organization," the company told employees in materials outlining the program.

Managers will assess their staff needs after they see how many people volunteer to retire and decide on "involuntary separations" after that, the company said.

It said "most, if not all, business units and divisions will separate non-union colleagues involuntarily during the Special Separation Program's terms."