(Reuters) - Staples Inc (>> Staples, Inc.) said it would give itself three more months before calling off its proposed $6.3 billion-acquisition of Office Depot Inc (>> Office Depot Inc), giving the companies time to fight an antitrust lawsuit with the Federal Trade Commission.

Staples said on Wednesday it would extend the termination date of the proposed acquisition to May 16 from Feb. 4, the previous deadline to settle antitrust issues.

The FTC sued to block the deal in early December, arguing the combination would control 70 percent of the U.S. market for office supplies purchased by large national customers.

Staples has accused federal regulators of applying antitrust laws in a "misguided" way to try and block the deal to merge the two biggest U.S. office supplies retailers.

The previous termination date of Feb. 4 marks a year since Staples offered to buy Office Depot to better compete with online and big box retailers such as Amazon.com Inc (>> Amazon.com, Inc.) and Wal-Mart Stores Inc (>> Wal-Mart Stores, Inc.).

(Reporting by Yashaswini Swamynathan in Bengaluru; Editing by Savio D'Souza)