The aim of this study was to describe prerequisites for online collaboration for user participation in co-design of online digital services as perceived by people with impairments and to develop requirements for how online collaboration should be designed to be accessible for all participants. An exploratory study was conducted in parallel to activities in two co-design projects. Researchers, accessibility experts, designers and 31 members of disability organisations participated. All participants had lived experience of impairments. Data was co-analysed by all participants using a qualitative thematic analysis with an inductive approach. Sixty-three requirements for accessible online collaboration were identified pertaining to four themes: digital tools and accessibility; preparation of an online collaboration activity; performing and participating in an online collaboration activity; and documenting and evaluating an online collaboration activity. Conclusion: the co-design process can be strengthened by transition to online collaboration, owing to the possibility of having more frequent interaction, economising the participants' energy and the design process being more transparent. Using accessible online tools, careful planning, and meeting preparation, and establishing a trustful and convivial atmosphere during each activity, are the cornerstones for accessible online collaboration. People with impairment can participate in online collaboration if the activities meet accessibility requirements.