The suspects say they fear the force will officially lay charges against them, RTHK reports.

The group, including Roy Tam, Lester Shum, Ventus Lau, Jeffrey Andrews, Tiffany Yuen, Shun Lee, Fergus Leung and Hendrick Lui announced on social media on Friday that they had been told to attend police stations at two o'clock on Sunday.

American human rights lawyer John Clancey said he had also been called in.

The group had initially been released on police bail until April.

They were among more than 50 people arrested on suspicion of "subverting state power" for their involvement in primary elections in July last year that were intended to choose candidates for Legco polls that never took place in the end.

Others arrested included former Hong Kong University legal scholar Benny Tai, who initiated the primaries, Andrew Chiu who organized them, as well as former lawmakers James To, Wu Chi-wai, Andrew Wan, Lam Cheuk-ting, Helena Wong, Au Nok-hin, Chu Hoi-dick, Alvin Yeung, Kwok Ka-ki, Jeremy Tam and Gary Fan.

Activist Joshua Wong, who is currently serving prison time on incitement charges, was also among those arrested.

Lau and Leung said they believe they will be charged, adding that the chances of them being granted bail will be extremely slim.

Officials had said the primaries were an attempt by the camp to win enough seats to "paralyze the government".