American Airlines is not happy with Qatar Airways' intent to invest.
American Airlines CEO Doug Parker sent a letter to employees on Thursday in response to Qatar Airways announcing their offer to acquire a 10 percent stake in the company.
In the letter, Parker uses the word "puzzling" to describe Qatar Airways' intention to invest and specifically points out "illegal subsidies" as the reason behind his criticism.
"While anyone can purchase our shares in the open market, we aren't particularly excited about Qatar's outreach, and we find it puzzling given our extremely public stance on the illegal subsidies that Qatar, Emirates and Etihad have all received over the years from their governments," Parker wrote.
Parker, a longtime critic of Gulf carriers such as Qatar, continued by saying the company is still maintaining efforts to stand against illegally subsidized companies.
"While today's news for some of our team may be puzzling, at best, and concerning, at worst, here's what we know for sure: We will not be discouraged or dissuaded from our full court press in Washington, D.C., to stand up to companies that are illegally subsidized by their governments," Parker wrote.
Parker later told CNBC that Qatar has not explained its intent to invest, other than that it would be a passive stake.
While some had speculated that Qatar may want to invest in an attempt to soften American resistance to the expansion of foreign airlines in the U.S., Parker dismissed the idea that such a move would be effective.
"If that is their motivation, it is misguided and ill conceived," Parker told CNBC. "All this is doing is strengthening our resolve to defend our airline, which we will continue doing vigorously."
The CEO ended the letter by assuaging investors and employees by explaining that even if Qatar decides to invest, their investment will not be enough to influence American's management or strategy.
"And do not worry, per U.S. law, no foreign entity can own more than 25% of a U.S. airline," Parker wrote. "So there is no possibility that Qatar will be able to purchase enough of American to control or influence our Board, management or our strategy."
Read the full letter below.
— CNBC's Phil LeBeau contributed reporting.