They say Walkers plans to launch his long-expected run by filing the necessary paperwork today. Walker's official kickoff is expected July 13.
The aides spoke on condition of anonymity because they weren't authorized to publicly discuss the launch ahead of the filing.
The 47-year-old Walker is in his second term as governor. He won a recall election in 2012 after angering union members by signing a law curtailing their collective bargaining rights.
Before jumping into the 2016 race, Walker had been waiting for state lawmakers to finish work on a new budget. But with progress in the Wisconsin Legislature stalled, Walker is moving ahead with his campaign.