AAP has immediately sought an apology from them in writing and also asked them to publish the same 'along with true and correct facts' in newspapers within 24 hrs.
The notice alleged that the "offending publication (pamphlet)" was issued either by them (BJP and Gautam Gambhir) or the persons authorised by them.
"In view of the above, you are hereby called upon to render immediately a complete, express, unqualified and unambiguous apology to our client, its leaders and its candidate for inflicting the libel upon them, which must be tendered to our client personally in writing by you as well as well as printing the same along with true and correct facts in Delhi as well as across India within 24 hours," the legal notice by AAP read.
It also warned that if they fail to do so, legal proceedings both criminal (for the "offence" of criminal defamation and civil suit(for recovery of damages) will be initiated against them.
This comes a day after Gautam Gambhir had sent defamation notice to AAP leaders-- Arvind Kejriwal, Manish Sisodia, and Atishi demanding an unconditional apology from making "defamatory" comments against him.
The row started with AAP leaders accusing Gautam Gambhir of circulating pamphlets with derogatory and casteist remarks against his rival candidate Atishi.
On Thursday, Delhi's deputy chief minister Sisodia had accused the cricketer-turned-politician of distributing pamphlets in an attempt to defame Atishi.
"Language in this pamphlet, distributed in East Delhi, is so abusive and low that everybody will feel ashamed while reading it. This letter with derogatory remarks is distributed by Gautam Gambhir to make himself win. We never, in our worst dream, had thought that he (Gambhir) would stoop to this low to win polls," Sisodia had said.
AAP chief Kejriwal also reiterated the charges and raised similar questions.
"How can women expect safety if people with such mentality are voted in? Atishi, stay strong. I can imagine how difficult it must be for you. It is precisely this kind of forces we have to fight against," he had tweeted.
Gambhir and Atishi are in a three-cornered battle along with Congress candidate Arvinder Singh Lovely from the east-Delhi parliamentary constituency which will go to polls on May 9.