"Working. It is not just an ordinary meal," Anutin Charvirakul posted in a message accompanying pictures on his Facebook page.
Those pictures, posted on Tuesday night, showed the Bhumjaithai leader having lunch with Democrat secretary-general Chalermchai Sri-on and Montree Panoinon, a Democrat MP for Prachuap Khiri Khan.
The images reiterated the political manoeuvres of the Bhumjaithai Party, which is reaching out to other parties undecided on whether they will join the Palang Pracharath Party-led camp to give the premiership to Prime Minister Prayut Chan-o-cha or side with the anti-regime faction spearheaded by the Pheu Thai Party.
There has been speculation that Bhumjaithai plans to form a core alliance with the Democrats, giving the two parties a combined 103 seats in Parliament.
The meeting was the first for Mr Chalermchai since being selected as the Democrat secretary-general under the leadership of Jurin Laksanavisit.
Mr Montree said on Wednesday the two parties had agreed to form a political alliance to fulfill the political promises they made to voters during the election campaign.
Bhumjaithai was targeting the Transport, Public Health, and Tourism and Sports ministries, while the Democrats favoured cabinet seats in the Interior, Commerce and Energy ministries, he added.
The Public Health Ministry would enable Bhumjaithai to pursue its policy of promoting the commercial cultivation of marijuana, while the Tourism and Sports Ministry could promote its tourism policy, Mr Montree said.
The Democrat MP for Prachuap Khiri Khan did not mention the reason for Bhumjaithai to oversee transport affairs. But the Transport Ministry has been one of the key targets for Bhumjaithai in the past. The party was in charge of transport when it was part of the Democrat-led coalition government led by then prime minister Abhisit Vejjajiva.
The Democrat Party wants to solve the problem of declining agricultural prices for farmers, said Mr Montree, who shared the pictures on his own Facebook account.