According to sources, top Congress leaders held consultations with leaders of other non-NDA parties and discussed the joint strategy.
A total of 18 opposition parties, including the JD-U will meet tomorrow to evolve its strategy at a meeting hosted by Congress President Sonia Gandhi in Parliament library.
The party vice chief Rahul Gandhi besides a host of leaders from other parties like the NCP, RJD, Left, TMC, SP, BSP, DMK and other smaller parties are also likely to attend.
The parties are also likely to discuss the opposition floor management for the monsoon session of Parliament, which starts on July 17, as it comes in the wake of raids on RJD chief Lalu Yadav.
Non-Congress opposition parties are not averse to discuss candidature of a contender from the grand old party for the August 5 vice presidential poll, sources said.
With the presidential poll being a 'Dalit versus Dalit contest', the idea of fielding a candidate from the community may not be considered strongly, the sources said virtually ruling out the possibility.
The parties though continued to maintain today that no names were being discussed among them "even informally" for the election, which is stacked heavily in the favour of the NDA which has 550 of the total 790 Parliamentarians on its side.
The sources said that after the opposition lost out in announcing its candidate to the ruling NDA, it might declare its candidate tomorrow before the ruling alliance does.
The election will be held as the tenure of vice president Hamid Ansari will end on August 10.
Polling, if required, will take place on August 5 and the votes will be counted on the same evening.
Vice President Ansari had secured 490 votes during the last vice presidential polls held in 2012. The opposition's candidate then, Jaswant Singh, had gained 238 votes.
So far, four Vice Presidents have been elected unopposed --first Vice President of India S Radhakrishnan (1952 and again in 1957), Mohammad Hidyatullah (1979) and Shankar Dayal Sharma (1987).