Xerox CEO John Visentin sent a letter to HP on Tuesday announcing plans to take its $33.5 billion buyout directly to shareholders.

"While you may not appreciate our 'aggressive' tactics, we will not apologize for them," Visentin wrote in the letter. "The most efficient way to prove out the scope of this opportunity with certainty is through mutual due diligence, which you continue to refuse, and we are obligated to require."

"We plan to engage directly with HP shareholders to solicit their support in urging the HP Board to do the right thing and pursue this compelling opportunity," he added.

Activist investor Carl Icahn, who owns a 10.6% stake in Xerox and recently bought a $1.2 billion stake in HP, has pushed for a merger.

The two companies have been sparring ever since HP's board of directors unanimously rejected a proposal from Xerox to acquire the company for $22 per share in cash and stock. HP said the offer is not in the best interest of shareholders and would undervalue HP. Xerox execs initially gave HP's board a deadline of Nov. 25 to reconsider the offer.

HP announced in October plans to cut between 7,000 and 9,000 jobs by the end of fiscal 2022 as part of a broader restructuring plan that it estimates will save $1 billion a year. The cuts would amount to nearly 16% of its 55,000 employees across the world, according to data from FactSet.

"The potential benefits of a combination between HP and Xerox are self-evident," Visentin wrote. "Together, we could create an industry leader — with enhanced scale and best-in-class offerings across a complete product portfolio — that will be positioned to invest more in innovation and generate greater returns for shareholders."

Spokespeople for HP and Xerox were not immediately available to comment on the letter. HP reports its fourth-quarter earnings on Tuesday after the bell, when it may issue a response.

Read Xerox CEO John Visentin's full letter below.

Dear Chip and Enrique, Your refusal to engage in mutual due diligence with Xerox defies logic. We have put forth a compelling proposal – one that would allow HP shareholders to both realize immediate cash value and enjoy equal participation in the substantial upside expected to result from a combination. Our offer is neither "highly conditional" nor "uncertain" as you claim. It does not contain a financing contingency, and the combined company is expected to have an investment grade credit rating. The potential benefits of a combination between HP and Xerox are self-evident. Together, we could create an industry leader – with enhanced scale and best-in-class offerings across a complete product portfolio – that will be positioned to invest more in innovation and generate greater returns for shareholders. The market clearly understands the industrial logic of this transaction. HP and Xerox shares are up 9.5% and 6.6%, respectively, since the date our proposal was first made public. We have already received inquiries from several HP shareholders and are encouraged by their interest in our offer. Nevertheless, rather than engage with us in three weeks of customary mutual due diligence, HP continues to obfuscate and make misleading statements. It is important that we correct, for your benefit and that of HP's shareholders, a few of the mischaracterizations from your last letter. On February 5, 2019, Xerox announced a three-year strategic plan that was built on four initiatives: (i) optimizing operations, (ii) driving revenue, (iii) reenergizing innovation and (iv) focusing on cash flow and capital returns. We are already outperforming this plan. Through the first nine months of 2019, we have increased our guidance for adjusted earnings per share and free cash flow while also increasing investments in innovation and our core business, which is why our stock is up 96% year-to-date.

Your comment regarding total contract value is little more than a diversion. Your own public disclosure states that backlog information is "not a meaningful indicator of future business prospects" or "material to an understanding of our overall business."

It is possible that the modest, expensive and time-consuming cost savings included in the restructuring plan you announced on October 3, 2019 (only $1 billion over three years at a cost of $1 billion in restructuring charges), has resulted in a lack of confidence in HP's ability to realize the $2+ billion of synergies your team previously agreed could be achieved in a combination.

We monetized our illiquid interest in Fuji Xerox at over 20 times 2019 expected aggregate cash flow while favorably restructuring the terms of our sourcing relationship with Fuji Xerox to ensure continuity of supply, protect our high-value intellectual property and provide strategic flexibility. There is no "hole in Xerox's portfolio" as a result of those transactions – just significantly more cash to support growth and greater flexibility in our sourcing terms. While you may not appreciate our "aggressive" tactics, we will not apologize for them. The most efficient way to prove out the scope of this opportunity with certainty is through mutual due diligence, which you continue to refuse, and we are obligated to require. We plan to engage directly with HP shareholders to solicit their support in urging the HP Board to do the right thing and pursue this compelling opportunity. Sincerely, John

Vice Chairman and CEO

Xerox Holdings Corporation

— CNBC's Emma Newburger and Lauren Feiner contributed to this report.