Portuguese higher education institutions need to diversify their educational offer in order to adapt it to new audiences for which the forms of teaching and learning including online education are increasingly attractive. However there are few studies related to how teachers perceive the adoption of forms of teaching and learning that include online teaching. In this study, conducted by research by questionnaire in 11 Portuguese private higher education institutions, we sought to identify the constraints of higher education teachers regarding adoption of online learning. The results show that increasing the time they have to devote to teaching activities is the main constraint reported by teachers in relation to the adoption of online learning. Exploratory factor analysis identified six dimensions related to the constraints of teachers: increased academic work; institutional support; social recognition of online learning; staff availability and peer support; online interaction; problems related to copyright. Teachers experience little receptivity and a high prejudice towards online education, and, the most part, has reservations about the impact that it can have on their professional development. The creation of motivational strategies for the improvement of the technological and pedagogical skills can help teachers engage in forms of distribution that include online teaching