Opposition parties are planning to meet the President after the elections are over.

Highlights 21 parties to show letters of support for an alternative government

Step to ensure single largest party doesn't get chance: sources

Lok Sabha has 543 elected members and the majority mark stands at 272

With two more rounds of elections to go, opposition parties are planning to meet the President after the elections are over, to impress upon him not to call the single largest party to form the government in case of a split verdict, sources said.

Twenty-one political parties that are opposing the BJP at the centre plan to sign a letter, saying once election results are out, they will be ready to show the President their letters of support for an alternative government.

Sources said the reason for this unusual step is to ensure that the President does not give the single largest party an opportunity to attempt and break regional parties and alliances.

The Lok Sabha has 543 elected members and the majority mark stands at 272.

In the 2014 national elections, the BJP won majority - a first in decades - with 282 seats. The combined strength of the NDA was 336 seats in the Lok Sabha.

In 1998, President KR Narayanan had insisted that Atal Bihari Vajpayee produce letters of support before he was called to form government and seek a vote of confidence on the floor of the house. That time, the BJP had won 178 seats, the alliance had 252 members -- a wafer thin majority even with outside support. The government collapsed after 20 months, when it lost the vote of confidence by a single vote.

The last five years have seen much controversy over government formation in states like Manipur, Goa and most recently, Karnataka over whether a post-poll coalition or the single-largest party should be asked to form government.

In Karnataka, the BJP had protested when, in a deft post-poll manoeuvre, the Congress tied up with HD Kumaraswamy's Janata Dal Secular. Till the last minute, state BJP chief BS Yeddyurappa had insisted that his party should be invited to form government and it would prove majority on the floor of the assembly. The initiative stopped amid allegations of attempts of horse-trading by the BJP.

For the Lok Sabha polls, while there is no formal coalition, 21 parties have banded together at the national level to take on the BJP. Even so, there are indications that other combinations are being contemplated, the chief among which is a non-Congress, non-BJP front under the initiative of Telangana Chief Minister K Chandrashekar Rao.

The last round of elections will be held on May 19. The counting of votes will take place on May 23.