Foreign shareholding in banking activities is limited up to 49% of total voting capital and the majority of the board of directors must be Thai citizens.
"[…] CHAPTER 2 - STRUCTURE OF FINANCIAL INSTITUTION
DIVISION 1 - Shares and Shareholders […]
Section 16. The amount of shares of a financial institution held by persons of Thai nationality must not be less than seventy-five per cent of the total number of voting shares sold and the number of its directors who are persons of Thai nationality must not be less than three-fourths of the total number of directors. Where the Bank of Thailand deems appropriate, the Bank of Thailand may permit persons of non-Thai nationality to hold shares up to forty-nine per cent of the total number of voting shares sold, and may permit the number of directors of non-Thai nationality to be more than one-fourth but less than one-half of the total number of directors.
Where it is necessary to rectify the operation’s condition or to enhance the stability of any financial institution or for the stability of the financial institution system, the Minister may, with the advice of the Bank of Thailand, grant relaxation  for any financial institution to have the number of shares or directors other than that prescribed in the second paragraph. In this regard, rules or time clause on the relaxation may also be prescribed. [...]"(FINANCIAL INSTITUTIONS BUSINESSES ACT, B.E. 2551 (2008))
FINANCIAL INSTITUTIONS BUSINESSES ACT, B.E. 2551 (2008), Section 16.
[<a href="https://www.bot.or.th/English/AboutBOT/LawsAndRegulations/SiteAssets/Law_E24_Institution_Sep2011.pdf">Act</a>]