US office supply chain Staples has offered to buy the owner of Office Depot for $2.1bn, making a third push to acquire its smaller rival after competition regulators thwarted its previous efforts to combine America’s two largest bricks and mortar stationery retailers.

Staples, owned by private equity group Sycamore Partners, said it would pay $40 per share in cash for ODP, its longstanding competitor. The offer represents a more than 60 per cent premium to the average closing share price for ODP over the past 90 days, the group said in a statement. Shares in ODP rose 19.4 per cent in New York on Monday.

The Federal Trade Commission ruled four years ago that the merger of Staples and Office Depot, which was then worth about $6.3bn, would undermine the interests of corporate customers, curtailing their choice in the office equipment market. Regulators had blocked an attempt in 1997 to combine the two companies under the proposed “Staples the Office Depot” brand.

The latest effort to revive the deal may become a test case for whether US antitrust regulators believe the meteoric rise of ecommerce group Amazon has been sufficiently game-changing for the retail industry for them to now permit such a tie-up.

Amazon’s growing corporate customer base has challenged the grip that Staples and Office Depot have had on the market. Walmart and other discount chains have also encroached on to their territory.

Changing customer needs for the modern office have added to the pressure. The rise of email has reduced demand for paper and printer ink, for instance.

The decision over whether to approve any deal could also be an important test for Joe Biden’s incoming administration. While Democratic presidents have historically pushed for tougher antitrust enforcement, the increasing heft of Amazon has caused growing concern.

Staples was taken private four years ago by Sycamore in a $7bn deal and split in two: a highly regarded office supply division, and a store chain that analysts said faces many of the same challenges as other retailers hit by online competitors and shifting consumer behaviour.

It said in a statement on Monday that it could increase its offer for ODP if its competitor agreed to sell some of its assets, including CompuCom, the business it acquired in late 2017 for $1bn.

ODP said it was “carefully reviewing” the proposal. The takeover target noted “potential antitrust and other regulatory challenges” associated with the mooted combination, highlighting that its would-be suitor told ODP’s directors in a letter that it expected the regulatory process to take at least six months.

Challenges in the retail sector have remained intense since the previous merger attempt, and during the pandemic bricks and mortar chains across the US have struggled to attract customers.

Still, office suppliers have held up better than other retailers thanks to the recent working from home boom, which has fuelled sales of computers, printers and other equipment.

Shares in ODP, which has 1,200 stores and owns the OfficeMax chain, gained about 22 per cent in 2020.

Even so, the company has been far from immune from the effects of coronavirus restrictions, which have hurt sales at its business-to-business division. Third-quarter revenues across the group declined 9 per cent year on year to $2.54bn.