The contract covering 15,000 Philadelphia public school teachers has expired without a new agreement being reached.
Negotiations between the state-run School District of Philadelphia and the Philadelphia Federation of Teachers are still continuing after the expiration of the old collective bargaining agreement at midnight.
The state's largest district is trying to achieve more than $100 million in concessions from the union as it works to close a $304 million deficit. That deficit resulted in nearly 4,000 layoffs of teachers, administrators, secretaries and counselors and the ending of arts programs and extra curriculars. The teachers have blamed big cuts in state aid for much of the district's financial problems.
Fifty-million in emergency funding has been promised to the district which resulted in the rehiring of 1,000 staff members.
Classes for the city's 190,000 traditional and charter school students are scheduled to begin on Sept. 9.
Both sides released statements early Sunday saying they were continuing to work toward a new deal.
Last week, Philadelphia Federation of Teachers President Jerry Jordan said that his group is ready to make concessions, but would not specify exactly what those concessions are.
"What we are proposing is not a long-term solution, just trying to piece together a way to open schools safely," Jordan said.