The Arvind Kejriwal-led party also demanded a probe into BJP IT cell chief Amit Malviya's tweet.
"The way EC is working one-sided in favour of the BJP, this has not happened in its history," Sanjay Singh, AAP MP and spokesperson said.
"The EC has become BJP's institution and its subordinate," he alleged.
Ahead of the official announcement by Election Commission, Mr Malviya had tweeted that voting would be held on May 12 and the counting on May 18. He was correct about the day of the voting, but got the counting date wrong. The counting would be held on May 15.
The Election Commission has set up a committee to probe the leak.
AAP's fresh attack on the poll panel comes nearly a week after the Delhi High Court set aside the Election Commission's order to disqualify 20 party lawmakers for allegedly holding offices of profit.
Suggesting that all parties should unite over the issue, Mr Singh said AAP will approach all the opposition parties to stop the "BJP from doing whatever it wants".
"All opposition parties should come together to oppose the dictatorial tendencies of the BJP government," Mr Singh said.
Questioning the decisions of the Election Commission in the case of deferring the assembly elections in Gujarat and disqualification of AAP lawmaker's, senior AAP leader Ashutosh claimed, "The EC is working at the behest of the BJP".