The 34-year-old Sohn is expected to appear Friday in U.S.
District Court in Bridgeport. A telephone message left with his attorney, Philip Russell, was not immediately returned.
Shays, a moderate Republican who served 10 terms in Congress, narrowly lost to Democrat Jim Himes in November 2008 in the race for the 4th District in southwestern Connecticut that he had represented for 21 years.
Just weeks after Shays was defeated, a post-election review of his campaign finances uncovered a series of irregularities.
Shays turned the matter over to federal investigators last December and filed documents in February with the Federal Election Commission that detailed $148,000 in theft from the 2008 campaign.
The reports showed more than $73,000 in direct unauthorized campaign checks made payable to Sohn and dozens of unauthorized ATM withdrawals totaling more than $58,000.
Shays, a champion of campaign finance reform, did not immediately return a call seeking comment Friday. Previously, Shays had called the alleged embezzlement "a serious and sad situation."
"If true, the actions of this individual represent a betrayal of my campaign, its supporters and the very things I stand for, but in no way do they reflect upon the incredibly dedicated and honorable service of my other staff members and extended family of volunteers and supporters," he said a year ago.
In July, Shays said the campaign also owed nearly $28,000 in unpaid payroll taxes from money that he said was siphoned off to cover up the embezzlement. Shays said the tax was owed because Sohn didn't put some employees into the campaign's payroll system, which would have automatically deducted the taxes.