Some court appearances will be delayed due to prison overcrowding, after ministers sparked an emergency measure.
The move seeks to manage the flow of people through magistrates' courts, the custody service and prisons.
It is happening because of what is described as "significant pressures on the prisons estate".
A solicitors group said many magistrates court cases will be affected as officials decide which defendants will be prioritised.
The move, called Operation Early Dawn, is expected to impact courts in England for around a week in regions where there is a lack of prison places.
In addition from next week, some prisoners will be released 70 days earlier than originally planned.
This is going up from 35 days, having previously been 18 days.
Government officials say the pandemic is partly to blame, because it led to an increase in the number of people being held in prisons for longer, awaiting jury trial.
Using the mechanism being activated this morning is not unprecedented, but it is acknowledged by those in government to be a significant move in response to a difficult situation.
A Ministry of Justice spokesman told the BBC: "To manage this demand we have brought on thousands of extra places at pace and will introduce strategic oversight of the transfer of remanded offenders from police custody to magistrate courts to maintain the running of the justice system.
"This government is categorical that dangerous offenders should stay behind bars, which is why new laws will keep rapists locked up for every day of their prison sentence and ensure life means life for the most horrific murderers."
The Criminal Law Solicitors Association said: "We are appalled of the state of our criminal justice system and have been campaigning on this from our inception and whilst we recognise the need for some action, this is a symptom of a systemic problem caused by more than 40 years of neglect of our criminal justice system."