FRAMINGHAM, MA—Staples Inc. said Tuesday it “carefully considers” all actions that would create shareholder value, without commenting on the merits of Starboard Value LP's call for it to merge with rival Office Depot. The New York City-based investment firm, which owns stock in both retailers, also took locally based SPLS to task for its delay in acting on a plan to separate the roles of chairman and CEO that shareholders approved this past June.

With Office Depot and OfficeMax having finalized their merger in November 2013, the office-supply retail sector has just two superstore chains left. Combining them, Credit Suisse says in a report quoted in Starboard's letter, “makes significant financial and operational sense.”

A merger, according to Credit Suisse, would create “multiple years of earnings growth from synergies, reversing what has been a negative trajectory for Staples.” That trajectory began to reverse itself when speculation began last September about a SPLS merger, according to Starboard's letter, with shares in the retailer up more than 50%.

Conversely, pursuing a standalone strategy “has resulted in a 31% decline in earnings per share” for SPLS, according to the Starboard letter made public Tuesday over the signature of CEO Jeffrey C. Smith.  “Without a combination with Office Depot, we would expect Staples' share price to decline to reflect the company's standalone value. If this occurs, shareholders will be left then to evaluate Staples based only on its poor five-year share price performance, poor corporate governance and excessive executive compensation.”

And while SLPS is already the larger of the two remaining superstores in its space, a merger with Office Depot “would create an industry-leading office supply retailer that could more effectively compete against larger retailers and online competitors,” according to the Starboard letter. “The magnitude of value creation from such a business combination far exceeds anything that either company could achieve on a standalone basis.”