Lorraine Michael said she was shocked by the letter she received in an email over the weekend after returning from vacation, adding she has no plans to resign from her post.
"I certainly felt betrayed," the 70-year-old leader said in an interview Tuesday.
"That may sound like a strong word, but I had this sense of betrayal that caucus didn't feel that they could sit down and talk with me about the contents of the letter first. I thought we certainly had a good enough relationship, we haven't backed off from other tough discussions."
A caucus spokeswoman said the letter asks for a leadership convention next year to ensure party renewal ahead of a provincial election in 2015. Jean Graham said the letter was signed by all four caucus members — Dale Kirby, Gerry Rogers, George Murphy and Christopher Mitchelmore.
Michael, a former nun, has led the NDP since May 2006 and was first elected to the provincial legislature in a byelection in November that year in the St. John's riding of Signal Hill-Quidi Vidi.
The NDP finished second in the popular vote under Michael's leadership in the 2011 provincial election and won five seats, three more than its previous high in the legislature.
Michael said the letter was the first time she heard of any issues regarding her leadership from caucus colleagues.
"I have no problem with the caucus wanting renewal of the party and preparing for 2015 and doing our planning in a way that's going to strengthen the party and get good candidates," she said. "This is an ongoing discussion and I'm totally in agreement with that."
But she said the content of the letter came "out of the blue," adding that she has been performing well in polls.
"To have a letter questioning the leadership was rather startling. I had no reason to believe this was an issue."
Michael said she met with the party executive Monday and they support her leadership. She said she has already met with some members of the caucus, but intends to meet with the whole group this week in hopes of resolving any issues and coming to a mutual agreement.
"I'm not sure what people are totally thinking and I'm not sure what they're feeling," she said.
"We have to meet face-to-face, we have to start talking, we have to do what I think should have happened instead of a letter. ... We have to put all the cards on the table and not hold back, and I trust that we can do that."
The Progressive Conservatives hold 35 of 48 seats in the provincial legislature. The Liberals have seven, while the NDP have five. There is one vacant seat.