Barnes & Noble cut prices on three models of its Nook e-reader and tablet devices on Sunday, ahead of the peak of back-to-school shopping and amid speculation that its rival, Amazon.com, was preparing to introduce a new version of its Kindle Fire tablet.

Barnes & Noble, the largest American bookstore chain, said it had reduced the retail price of its Nook tablet with 16 gigabytes of memory to $199, from $249.

The company also shaved $20 off its eight-gigabyte model, to $179. And Barnes & Noble lowered the price of its Nook Color by $20, to $149.

The new prices went into effect on Sunday.

The Nook has given the chain 27 percent of the American market for e-books, Barnes & Noble has said. Amazon is the market leader with about 60 percent of e-book and e-reader sales.