The US Department of Justice has released a copy of the legal memorandum justifying President Obama's recess appointments of Richard Cordray and three new members of the National Labor Relations Board.
The document says periodic pro forma sessions where no business is conducted do not negate the president's power to bypass the Senate in making appointments.
The memo states: "in this context, the President therefore has discretion to conclude that the Senate is unavailable to perform its advise-and-consent function and to exercise his power to make recess appointments." [Emphasis added.]
Assistant Attorney General Virginia Seitz, who wrote the opinion, made the distinction that the Senate "could remove the basis for the President’s exercise of his recess appointment authority by remaining continuously in session and being available to receive and act on nominations, but it cannot do so by providing for pro forma sessions at which no business is to be conducted."
The entire memo can be found on the Department of Justice's webpage here.