India’s Jet Airways on Monday grounded four aircraft as it failed to pay the lease for renting them — the latest in a series of financial challenges hurting the airline.

Jet Airways, once the number two airline in India, said that it is “actively engaged” with aircraft lessors, as it informed the National Stock of India that it is grounding aircraft “due to non-payment of amounts outstanding to lessors.”

Jet Airways did not elaborate on which routes will be affected or how long the grounding is for. It has, however, cancelled flights to and from Abu Dhabi for an indefinite period, due to what it described as “operational reasons.”

“Jet Airways has cancelled all their flights from Abu Dhabi with immediate effect from March 18 due to operational reasons,” Etihad Airport services informed its passengers on Sunday, according to Indian media reports.