Updated with comments from an attorney. 

A new maneuver by Staples (SPLS)  in its bid to buy Office Depot  (ODP - Get Report) may still not prove enough to appease regulators.

On Tuesday, Staples and Office Depot announced an agreement to sell more than $550 million in corporate contract business and related assets to office supplies wholesaler Essendant. Essendant will pay Staples approximately $22.5 million for the business. The deal will only go through if the merger between Staples and Office Depot is completed. 

"We're pleased to reach this agreement with Essendant as we continue to work to complete the acquisition of Office Depot," said Ron Sargent, chairman and CEO of Staples in a statement. Sargent added, "Our agreement with Essendant strengthens a national competitor, further enables independent office products dealers and helps minority and woman-owned businesses compete for national commercial customers."

Shares of Staples popped about 6.3% in after hours trading Tuesday as investors wagers the deal moved the two retailers closer to joining forces. In early trading on Wednesday, Staples share were up about 3%.  

While the sales agreement formally demonstrates that Staples is serious about trying to alleviate competitive concerns, Staples previously noted that a proposal to divest an even larger amount of commercial contracts was rejected by regulators.

In a statement on Dec. 21, Staples said the Federal Trade Commission (FTC) rejected its proposal to divest up to $1.25 billion of commercial contracts in order to gain approval to acquire Office Depot. According to Staples at the time, the FTC did not issue a counter proposal. The company said it was willing to continue negotiations with the FTC to reach a settlement that addresses antitrust concerns, while also noting that it's pursuing the transaction through litigation.

An administrative trial to decide whether or not the deal can go through is scheduled to begin on May 10, 2016.

In effect, Staples has decided to sell about half of the business it said it would to satisfy regulatory concerns. With regulators believing the sale of $1.25 billion in commercial contracts by Staples would not be enough to keep competition fair in the office supplies space, it's unlikely that $550 million will satisfy their appetite.

"Based on the litigation posture and the hearing just a few weeks away, Staples must be of the view that this divestiture will move the needle towards the judge blessing the transaction," said Andrea Murino, co-chair of Goodwin Procter's antitrust practice via email. "Otherwise, they would have had no reason to take the time, effort, energy to get it signed."

Murino added, "It's impossible to know how the FTC will react, but I suspect the FTC will still conclude this divestiture does not go far enough to resolve its concerns -- what this does do, however, is force the FTC to 'litigate the fix' -- in addition to proving how the acquisition will lead to a substantial lessening of competition, the FTC must also now prove that the remedy the parties have proposed doesn't go far enough."

Staples did not immediately return a request for comment.