Bishop Martin Jumoad of Isabela also told the Asian church news agency UCA News that he got text messages from Catholics saying they, too, had received threatening letters.
The letter had the names "Puruji Indama" and "Nur Hassan J. Kallitut" printed at the bottom and "mujahedin" under each name. The purported senders introduced themselves as "Muslim warriors" who "don't follow any laws other than the Quran," Islam's holy book.
They said Bishop Jumoad should choose to convert to Islam or give "jizya," Islamic tax, to their group in exchange for protecting him in the "place of Muslims."
If he refuses to convert or pay, the letter threatened "force, weapons or war may be used" against him. It warned him not to feel safe even if he is "surrounded by soldiers" and cited bombings in various cities.
Bishop Jumoad was given 15 days to respond, with two mobile phone numbers to contact.
"If we do not receive response from you, it means you will oppose," the letter added.
I haven't seen a report on this elsewhere in the media, they are probably too worried about the usual Muslim reaction to bad press.