This is the first concrete sign that Time Warner is determined to fight Fox CEO Rupert Murdoch if he decides to do an end run around the board in an effort to acquire the company. Directors adopted an amendment to TW’s by-laws, which took effect immediately, that makes it harder for a small group of shareholders to call a Business Leaders Gather For B20 Summit In Sydneyspecial meeting, Time Warner says in an SEC filing. Previously investors holding at least 15% of the total votes could demand a meeting. The change limits that right to “the Chief Executive Officer or a majority of the entire Board.” The fear was that Murdoch — or anyone — could have tried to stampede short-term investors into accepting a deal even if the board concluded that it would not serve their long-term interests.

Related: Bart & Fleming: Fox-TW Mania Means Banker Fees And Layoffs, Not Quality

Time Warner shares are down 1.6% in post-market trading following disclosure of the change. The company says that it intends to restore the 15% threshold at the 2015 annual meeting.

Related: Will Anyone Besides Rupert Murdoch Take A Run At TW?