Senators in the opposition are visiting Senator Leila De Lima in her detention cell at the Philippine National Police (PNP) Custodial Center in Camp Crame.
Senators in the minority bloc arrived at about 11 am on Monday.
They are Senate Minority leader Franklin Drilon and senators Francis Pangilinan, Risa Hontiveros and Antonio Trillanes.
De Lima has been in jail since February this year as she faces drug charges filed in Muntinlupa Regional Trial Courts.
Earlier, she had expressed her desire to join the Senate deliberations.
She recalled that in 2008, then Senate President Aquilino Pimentel allowed Senator Antonio Trillanes to join the proceedings.
Trillanes was in detention at that time but he participated in legislative proceedings through a teleconference.