Both Houses of Parliament have been hit by the expenses scandal
Six MPs and peers are expected to learn on Friday whether they face charges over their expenses claims.
Director of Public Prosecutions, Keir Starmer QC, will make an announcement at 1100 GMT.
In November police handed files on four Parliamentarians - whose identities were not confirmed - to the Crown Prosecution Service (CPS).
Two more files were handed over in December. The CPS said a decision on "a number of files" would be announced.
The Metropolitan Police have been investigating several cases in the wake of the MPs' expenses scandal, which broke in May last year.
There have been no arrests during the investigation although it is understood some people have been interviewed under caution.
The CPS has to decide whether there is a realistic chance of conviction in any of the cases.
If any were to face charges and be found guilty of fraud or false accounting, they could face maximum penalties of 10 or seven years in prison.
The news comes as Sir Thomas Legg, who carried out an audit of all past claims under the second homes allowance dating back to 2004, recommended that more than 370 MPs repay money amounting to £1.1m in total.