Seventeen opposition parties had come together against the BJP-led NDA during the presidential and vice-presidential elections a year ago and Sonia Gandhi has been holding occasional meetings to nurture the bonding.
According to sources, leaders of NCP, RJD, Samajwadi Party, Bahujan Samaj Party, Trinamool Congress, DMK and Left parties attended the dinner among others.
Posting a few pictures from the dinner meet, Mr. Gandhi tweeted, "Fabulous dinner tonight, hosted by UPA Chairperson, Sonia Gandhi Ji".
Sharad Yadav of the Bharatiya Tribal Party, Mohammad Salim of the Communist Party of India (Marxist), D Raja of the Communist Party of India, Jharkhand Mukti Morcha's Hemant Soren, All India United Democratic Front's Badruddin Ajmal, Kerala Congress (Mani) leader Jose K Mani, D Kupendra Reddy from the Janata Dal (Secular), NK Premachandran of Revolutionary Socialist Party and Indian Union Muslim League's PK Kunhalikutty were also in attendance. With all eyes on 10, Janpath lawns, participants said there was no structured discussion but only informal chats about politics on different tables involving leaders across party lines.
Sonia Gandhi, Rahul Gandhi, former prime minister Manmohan Singh, Ghulam Nabi Azad, Mallikarjun Kharge, Ahmed Patel, AK Antony and Randeep Surjewala were among the Congress leaders present.
The show of opposition unity would not stop at Congress leader Sonia Gandhi's dinner tomorrow, but would continue at NCP chief Sharad Pawar's residence at the end of this month, senior NCP leaders have said. The BJD and TRS that rule Odisha and Telangana respectively have also not been invited.
The meeting triggered speculation about the parties discussing strategy to unite against the BJP before the 2019 Lok Sabha elections, NDTV said.
"This dinner was not hosted for politics, but for amity and friendship".
Congress President Rahul Gandhi later said there was "much political talk" during the dinner meeting.
At a time when the government was not allowing Parliament to function, he claimed, it was obvious that leaders of various parties, who wanted to raise issues in national interest, would get together to discuss the current political situation.
Rashtriya Janata Dal leader Tejashwi Yadav said the the effort is on to get the opposition united.
He accused the government of running away from debate in parliament on the Rs 12,600 crore PNB fraud case as also failing to tackle unemployment and problems of farmers.