Mayer's statement came just before CEOs representing the country's biggest tech companies, including Facebook CEO Mark Zuckerberg, testify before the House Judiciary Committee during an antitrust hearing.
"At TikTok we welcome competition," Mayer wrote. "We think fair competition makes all of us better. To those who wish to launch competitive products, we say bring it on. Facebook is even launching another copycat product, Reels (tied to Instagram), after their other copycat Lasso failed quickly."
Facebook launched its TikTok competitor feature Reels on Instagram in Brazil, Germany, France and India earlier this year; the app is expected to come to the U.S. sometime in August.
Mayer then accused Facebook of pushing attacks against TikTok "disguised as patriotism and designed to put an end to [TikTok's] very presence in the U.S."
U.S. officials and tech experts have expressed skepticism with TikTok's privacy and security practices since the app is owned by Chinese company ByteDance, and all Chinese-owned companies are required to comply with information requests from the CCP under a 2017 national security law.
Defense Secretary Mike Pompeo said earlier in July that the Trump administration is "looking at" an all-out ban on the app in the U.S., and Congress is considering legislation that would ban the app on all government-owned devices, citing data privacy concerns.
Facebook and other TikTok competitors have been stepping up competition upon reports of TikTok security fears.
Facebook has been offering financial incentives to convince TikTok influencers to switch to its competitor app, The Wall Street Journal reported Wednesday.
Another TikTok competitor called Triller has also raised commitments from investors totaling $200 to $300 million, two people with direct knowledge of the matter told FOX Business on Wednesday. Triller has also recruited a number of popular TikTok influencers and recently hired former TikTok star Josh Richards as its chief strategy officer.
Meanwhile, TikTok has nearly tripled its U.S. workforce in the last year and plans to add 10,000 more U.S. positions in the next three years. A number of those new hires include veteran privacy and security experts across U.S. political party lines.
Mayer also brought up TikTok's advertising practices in sharp contrast to Facebook.
"We are not political, we do not accept political advertising and have no agenda...," Mayer wrote. "Consumers can only benefit from the growth of healthy, successful platforms like TikTok and we will fight to continue to give American creators, users and brands an entertaining outlet for many years to come."
Additionally, Mayer announced that TikTok will be releasing the code for its content-moderation algorithm and called on all other social media platforms to do the same. Facebook, Twitter and Google have come under fire for some of their decisions to remove or label content from political users with large followings.
"TikTok has taken the first step by launching a Transparency and Accountability Center for moderation and data practices. Experts can observe our moderation policies in real-time, as well as examine the actual code that drives our algorithms. This puts us a step ahead of the industry, and we encourage others to follow suit," Mayer said.