Electors in the Congress presidential polls have been asked to put a tick mark against the name of their choice on the ballot paper after AICC president candidate Shashi Tharoor's team took up with the party's top poll body the issue of its earlier directive that voters write "1" to reflect their preference, citing that it may lead to confusion, sources said on Sunday.

In instructions for polling issued on Saturday, Congress central election authority chairman Madhusudan Mistry had said PCC Members "will mark '1' on the ballot paper against the name of the candidate and fold the ballot paper to put it into the ballot box".

Tharoor's team took up the issue with Mistry, stating that this may confuse the voters as Kharge is on serial number 1 and Tharoor on serial number 2 on the ballot paper and writing '1' in front of the name of the preferred candidate would put the latter at a "disadvantage, the sources said.

After Tharoor's team flagged this issue, Mistry is said to have conveyed to them that a tick would be accepted against the name of the preferred candidate instead of '1', they said.

Mistry had cited the party's constitution for writing '1' before the preferred choice.

Tharoor's team, however, pointed out that it was only meant for cases when there are two or more candidates and preferences have to be made.

Finally, Mistry on Sunday afternoon conveyed to Tharoor's team that a tick would have to be made instead of '1' to reflect the preferred choice, the sources said.

In a tweet, Tharoor said, "Breaking News: the @incIndia Election Authority has changed the requirement for a vote from writing '1' against the preferred candidate's name to a tick mark. Delegates please note a tick mark is needed in the box next to my name!"

The voters are instructed to put a tick mark in the box in front of the candidate whom they wish to vote for and putting any other symbol or writing a number would make the vote invalid, the message from Mistry's office being sent to delegates said, according to sources.

Tharoor's team has repeatedly flagged an uneven playing field and violation of directives by the party's central election authority.

They have also raised the issue of office bearers openly expressing support for Kharge, the latest being Rajasthan Chief Minister Ashok Gehlot.

Mistry last week had said that the Congress presidential polls will be held by a secret ballot and no one will get to know who voted for whom.

He had asserted that a level-playing field had been ensured for both candidates.

Polling for the party president's election will be held on Monday and counting will be taken up on Wednesday.