Some 14 police forces have sent files to the Crown Prosecution Service (CPS) over the past few months.
Each file relates to allegations concerning a candidate and an election agent and the number of people involved totals at least 30.
The allegations relate to busloads of Conservative activists sent to key seats whose expenses were reported as part of national campaign spending, rather than falling within the lower constituency limits.
The CPS said files had been received from the Metropolitan Police, as well as forces in Avon and Somerset, Cumbria, Derbyshire, Devon and Cornwall, Gloucestershire, Greater Manchester, Lincolnshire, Northamptonshire, Nottinghamshire, Staffordshire, West Mercia, the West Midlands and West Yorkshire.
The decision is expected to be announced around 11am.
If any General Election candidates are prosecuted, the Conservatives could choose to suspend them and replace them.
The decision comes just a day before the nominations for next month’s election close.