New Jersey Transit is giving its two largest rail unions until Friday to agree to a new round of contract negotiations, otherwise the agency says that it will need to prepare for a possible strike.

NJ Transit and the unions are already negotiating directly without a federal monitor.

A letter obtained by News 12 New Jersey indicates that rail service will run as usual for now, but a full shutdown could happen on July 16.

The current contact compromise was ratified only hours before the prior shutdown deadline in March. It included retroactive pay, a cap on employee's health insurance costs and a 21 percent salary increase over three years.

The unions involved are the Locomotive Engineers, Assistant Engineers and Engineer Trainees.