Archer Aviation (ACHR) shares sank 11% Monday when the manufacturer of electric vertical takeoff and landing (eVTOL) aircraft backed by United Airlines (UAL) announced it was doubling the number of common stock available and changed requirements for board membership and ownership.

In a regulatory filing, the company reported that in a special meeting of shareholders Dec. 20, investors voted in favor of amending the firm's certificate of incorporation "to increase the number of authorized shares of the Company's Class A common stock available for issuance from 700,000,000 to 1,400,000,000."

Shareholders also voted in favor of issuing Class A Common Stock to carmaker Stellantis (STLA) per an agreement made in August. 

Along with those decisions, shareholders approved "limits of the voting, ownership and control of the Company by persons who do not meet the definition of 'a citizen of the United States,'" as defined by federal law. In addition, Archer agreed to certain limitations on foreign ownership.

Despite today's losses, shares of Archer Aviation have added more than 60% of their value this year.