NEW YORK (CNN/Money) - Deutsche Asset Management Tuesday explained its vote for the merger of Hewlett-Packard Co. and Compaq Computer Corp., likely in response to accusations that it and other HP shareholders were pressured by HP into approving the union.

The news came a day after the U.S. Attorney and the Securities and Exchange Commission said they were investigating the hotly contested March 19 shareholder vote in response to a press report that suggested HP CEO Carly Fiorina and another executive may have discussed ways to coerce votes in favor of the merger.

"Deutsche Asset Management's decision to vote in favor of the merger of Hewlett Packard and Compaq was based upon presentations made by both Hewlett Packard management and Walter Hewlett and his team," Deutsche Asset Management said in a written response. "The decision was made by Deutsche Asset Management's proxy committee, [which] exercised its independent judgement solely in the interest of its clients. Deutsche Bank is cooperating in the civil litigation between Hewlett-Packard and Walter Hewlett."

Merger opponent Walter Hewlett has sued HP, saying its management threatened to lock Deutsche Bank, Deutsche Asset Management's parent company, out of future HP investment-banking business if it had voted against it.

Because of that pressure, Hewlett's complaint alleges, Deutsche Bank, which previously had indicated it would vote against the deal, at the last minute switched its votes in favor of it during a March 19 shareholder meeting. Deutsche Bank had until Tuesday refused requests to comment on Hewlett's suit.

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Hewlett is the son of HP co-founder William Hewlett and the only member of the company's board of directors opposed to the merger, though he has not been re-nominated for a seat on the board. Compaq shareholders approved the merger last month. It will be weeks before the HP vote is certified, but HP has claimed it won a narrow victory.

Shares of HP (HWP: Research, Estimates) rose nearly four percent in afternoon trading Tuesday. Shares of Compaq (CPQ: Research, Estimates) rose more than 3 percent.