"If Mamata Mayavati and Sasikala combine we in BJP will have real challenge in 2019 (sic)," Swamy said on Twitter.
A known critic of the saffron party, TMC chief Mamata Banerjee has been at the forefront in the opposition's bid to form a united front against the Prime Minister Narendra Modi-led NDA for 2019 elections.
Mayawati, on the other hand, formed an alliance with arch-rival Samajwadi Party in Uttar Pradesh and vowed to oust the saffron party from power in the Centre.
Sasikala is serving a four-year prison term a disproportionate assets case at the Parappana Agrahara jail in Bengaluru. Sasikala, the close aide and shadow of Jayalalithaa for almost three decades, was locked in a power struggle for the top post with then acting Chief Minister O Panneerselvam.