P&G's salvo comes weeks after Peltz's Trian Fund Management sought a board seat for the activist investor at the company, making P&G the largest company ever to face a proxy battle.
In a statement to shareholders, the maker of Tide detergent and Gillette razors said Peltz offered no new "actionable ideas" that the company hadn't already implemented.
""Why not?" is not a compelling rationale to add Mr. Peltz to the P&G Board. "Why not?" appears to be the extent of Mr. Peltz's reason for board membership. This is simply not a sufficient standard," Chief Executive David Taylor said.
"Joining P&G's board is not an entitlement."
Peltz, whose hedge fund Trian has amassed an about 1.5 percent stake in the company, launched the proxy battle, after five months of negotiations with P&G's management failed to get him a board seat.
The investor, who is being advised by former P&G CFO Clayton Daley, has been pushing the company to cut costs more efficiently as well as eliminate its "suffocating bureaucracy".
In a proxy filing on Monday, Peltz said Trian's analysis showed that a P&G cost-cutting program launched in 2012, aimed at saving $10 billion over five years, had no discernible impact on profit or sales growth.
He also said P&G's move to meaningfully cut spending on digital advertising would inflict long-term damage to the company's brands.
P&G, the world's biggest advertiser, retorted by saying that Peltz seemed "confused" with the company's digital ad spending plan, which was aimed at avoiding fraud and waste in the online advertising marketplace.
The company said these efforts helped it save $100 million in ineffective spending.
P&G also criticized Peltz for leaning on Daley, who was CFO of the company nearly a decade ago.
"This ... appears to be compounding Trian's fundamental misunderstanding of P&G today and the operating environment the company faces," Taylor said.
P&G's shares were up marginally in afternoon trading on Tuesday.
(Reporting by Siddharth Cavale in Bengaluru; Editing by Saumyadeb Chakrabarty)
By Siddharth Cavale