Con Ed has given the Ground Zero mosque an ultimatum: Pay the $1.7 million you owe in back rent, or we�ll terminate your lease and take back our property.

Con Ed and mosque developer Park51 have an unusual, uneasy alliance, sharing ownership of a site slated to be one of the most controversial projects in city history.

The utility owns a former substation on the western half of the property, at 51 Park Place, and the mosque developers own a five-story building on the eastern half. The buildings were connected years ago and used to house a Burlington Coat Factory store.

Park51, which leases the substation from Con Ed, wants the two buildings so it can knock both down and build a $100 million, 15-story community center.

But the plan hit a major obstacle in August when Con Ed raised the rent from $2,750 a month, a rate set in 1972, to $47,437 a month, retroactive to July 31, 2008, The Post has learned.

When the mosque failed to fork over the $1.7 million, the utility fired off a letter demanding the money by Oct. 4 and threatening to evict.

Park51 principals responded with a lawsuit to stop the increase, calling Con Ed�s rent demands �outrageous.�

�Whether it is bowing to political pressure or seeking to retain the valuable premises for itself, Con Ed appears intent on proceeding with its wrongful termination,� argued Sharif El-Gamal, the lead Park51 developer.

Gamal�s group bought the building at 45-47 Park Place in 2009 for $4.8 million and, at the same time, paid $700,000 for the lease at the substation.

Court papers show that the appraised price for the Con Ed property is $10.7 million. But Gamal contends Con Ed�s math was faulty when it calculated the rent, saying it owes only $881,519 in back rent and should have to pay $25,875 a month going forward.

Gamal got a court order to temporarily prevent Con Ed from ending his lease.

READ MORE: NY POST