The board of engineering firm Michael Baker Corp. has begun 2013 facing new pressure from stockholders who have sought for months to boost the publicly held firm's share value. The Pittsburgh company's board announced Jan. 7 that its "independent" members will now seek new "strategic alternatives," including an unsolicited buyout offer it received last month from a financial-firm investor. The tumult, which includes the ouster of CEO Bradley L. Mallory, may signal new challenges for the industry's public firms—particularly smaller ones—at a time of changing market conditions.