Shareholder Joseph Pirinea said on Monday he was pushing bond insurer Ambac Financial Group to hire an investment bank to review strategic alternatives.

Pirinea said the review should include the potential sale of its core business, Ambac Assurance, as well as share buybacks and paying “substantial liquidating dividends” to shareholders.

Pirinea, who has already sued Ambac over its exposure to bonds issued by Puerto Rico, said in a statement he would introduce a proposal seeking a review at Ambac’s annual meeting or at a special meeting of shareholders.

It was not immediately clear how many Ambac shares he owns. Pirinea’s name does not appear on the most recent lists of significant shareholders in Ambac.

Ambac was sued in June for allegedly concealing its exposure to losses on municipal bonds it insures, including about $2.5 billion issued by Puerto Rico.

The company was accused of knowing that it was likely to become liable for payments when the U.S. territory inevitably defaulted on its debt, but concealed that fact from investors, thereby artificially inflating the price of its shares.

Ambac’s shares, which have risen about 26 percent this year, were up 1.3 percent at $17.93 in morning trading. The company has a market capitalization of about $800 million.

This is not the first time this year that Ambac has faced off with an activist investor. Canyon Capital Advisors dropped a proxy fight in May following pressure from another large shareholder, Cornwall Capital Management LP.

Ambac has undertaken a series of steps to appease shareholders this year, including reining in costs and reaching a settlement with a residential mortgage-backed securities (RMBS) counterparty.