Gildan Activewear Inc. agreed to buy U.S. underwear maker Hanesbrands Inc. for about US$2.2 billion in cash and stock, in its largest ever acquisition.

Canada-based Gildan is offering Hanesbrands holders roughly US$6 a share, based on the companies’ closing prices on Aug. 11, according to a statement Wednesday. Including debt, the deal values Hanesbrands at about US$4.4 billion.

The transaction targets synergies at least US$200 million within three years, according to the statement, and be at least 20 per cent accretive to Gildan’s earnings per share.

Shares in Hanesbrands slid 7.4 per cent in premarket trading, after gaining 28 per cent on Tuesday following reports on the deal.