The political deadlock between the pro-junta and anti-military camps, with neither side having enough MPs to form a coalition, has increased speculation that the Democrat and Bhumjaithai parties could perform a "kingmaker" role.
The two parties together hold 103 seats in the House of Representatives, 148 short of a majority but enough to gain leverage against the rival coalitions.
The Democrats and Bhumjaithai won 52 and 51 MPs, respectively, but both remained undecided on which camp to join in the Parliament.
On Tuesday, Bhumjaithai leader Anutin Charnvirakul posted photos on Facebook of a working dinner with Democrat’s secretary-general Chalermchai Sri-on and Prachuabkirikhan MP Montri Panoynon.
“We’re working here, not just dining. It’s exactly like what we’ve said before,” Anutin wrote.
The photos showed the trio sharing a meal and Anutin and Chalermchai shaking hands, smiling.
This raised questions about whether the two parties would create an alliance to help form a coalition to end the political deadlock.