Tabula Rasa HealthCare has approved a 10% poison pill rights plan in response to Indaba Capital Management’s accumulation of stock over the last week. Indaba is running a campaign to remove Tabula Rasa’s chief executive and his wife, also a top executive at the healthcare technology company.

The shareholder rights plan was adopted following Indaba’s disclosure last week that it increased its stake to 25% of outstanding shares, up from 20%, Tabula Rasa said in a Tuesday press release.

The one-year poison pill prevents investors from acquiring more than 10% of Tabula Rasa, with Indaba being grandfathered at its current ownership level, but with no possibility of raising its stake.

“While we appreciate Indaba’s investment in TRHC [Tabula Rasa], we want to ensure that the board is able to fulfill its fiduciary duty to maximize the value of Tabula Rasa, which includes protecting TRHC from being controlled or acquired in a manner or at a price that are not in the best interests of our stockholders,” said Lead Independent Director Gordon Tunstall.

Markets reacted poorly to the news, with Tabula Rasa’s stock falling more than 5% in morning trading Tuesday in New York.

Last week, Indaba argued in a letter that Tabula Rasa CEO and Chairman Calvin Knowlton must be forced out, along with his wife, Orsula Knowlton, citing “abysmal corporate governance, dysfunctional boardroom, and sustained underperformance” under their rule. Indaba also targeted Tunstall, saying he should not lead Tabula Rasa’s independent board members since he has longstanding ties with the Knowltons.