Xerox said in a letter to HP’s board of directors that it will take its $33 billion takeover bid to HP’s shareholders if the company doesn’t reconsider Xerox’s acquisition offer by Monday.

Xerox Chief Executive and Vice Chairman John Visentin said in the letter on Thursday that Xerox is “very surprised” that HP’s board rejected the buyout offer of $22 a share, which comprises $17 in cash and 0.137 Xerox share for each HP share.

HP rejected Xerox’s offer Sunday as too low and not in the best interests of its shareholders. It expressed a willingness to discuss a deal to combine with its smaller rival, though, saying it needs more information about Xerox’s business, through a process known as due diligence.

Visentin said he finds HP’s reasoning for rejecting the buyout confusing, as HP’s financial adviser, Goldman Sachs, had set a $14 price target with a “sell” rating for its stock in October. Goldman Sachs said Thursday that the price target is no longer effective.

Xerox said its offer represents a 57% premium to Goldman’s price target and a 29% premium to HP’s 30-day volume-weighted average trading price of $17.

If the two companies aren’t able to agree on a mutual due-diligence process by 5 p.m. Eastern time Monday, Xerox said it will take its case directly to HP’s shareholders.

Xerox said it remains willing to devote the resources necessary to complete mutual due diligence over the next three weeks and confirm the cost and revenue benefits it sees if the two companies combine.

Xerox said it encourages HP “not to sanction further delay in light of our extensive discussions to date.”

Shares of Xerox rose 0.8%, and HP shares rose 0.4%.

The companies dominate different areas of the printer market and have been cutting costs as the need for printed documents declines. They had previously discussed combining forces but weren’t in talks when Xerox made the offer.

Xerox primarily makes large printers and copy machines, while HP mainly sells smaller printers and printing supplies. HP is also one of the biggest PC makers in the world, though its printer business is more lucrative.

The potential union has received the support of activist investor Carl Icahn, who told The Wall Street Journal this month that the combination is a “no-brainer” that would increase returns for shareholders of both companies.

Icahn has a long history with Xerox, in which he owns a 10.6% stake, and he revealed a 4.24% investment in HP that makes him its fifth-largest shareholder, according to FactSet.

Xerox said it will take its $33 billion takeover bid for HP to shareholders if HP doesn’t reconsider the offer.

The associated press