The party has announced the name of MLA Pandurang Madkaikar as its candidate, while the ruling BJP and its alliance partners have fielded Vishnu Surya Wagh.
"All the members...Are hereby directed to vote in favour of Pandurang Madkaikar..." the whip says.
"Any failure to comply with the direction will invite disqualification from being a member of Goa legislative Assembly as provided under the tenth schedule of the Constitution of India," the whip says.
BJP and its allies have 25 MLAs in 40-member Assembly while Congress has nine. Congress has enlisted the support of independents including Vijai Sardesai, Rohan Khaunte and Naresh Sawal.