CHICAGO (From news reports) -- Chatham Asset Management on Monday raised its offer for RR Donnelley & Sons Co to $10.25 per share, hours after the printing company reaffirmed that it was sticking to a merger with investment firm Atlas Holdings.

Chatham, which owns a 14.9% stake in RR Donnelley making it the largest shareholder, earlier this month had offered to acquire the remaining stock in the company for $9.10 per share.

RR Donnelley agreed to be taken private by Atlas for $8.52 per share in cash earlier this month, valuing the company at about $2.1 billion.

Earlier in the day, RR Donnelley said it had also received an alternative proposal from an unnamed party offering to buy the company for $10.00 per share in cash, but the printer maker continued to recommend the deal with Atlas as its go-shop period comes to an end.

The go-shop period allows the target company in an M&A agreement to seek out competing bids even after it receives an offer from the acquirer.