The bank's annual meeting is on Tuesday, and by far the most controversial matter up for vote is whether bank head Jamie Dimon should retain his chief executive role but be stripped of his chairman title. Investors that sponsored the measure, including a government workers' union pension fund, said the bank's CEO has too much sway over the board, and needs more oversight. Dimon has hinted that if he is no longer chairman, he may leave the bank.

Last week, the company that collects votes from investors, Broadridge Financial Solutions Inc, (BR.N) stopped telling the shareholders how votes had been cast so far for this and other measures. Investors use this information to determine how to tailor their campaigns. JPMorgan was not immediately available for comment.

Receiving the information at this late state is of limited use, said Dieter Waizenegger, executive director of the CtW Investment Group, which advises pensions that were voting against the bank in a separate measure regarding the reelection of directors.

"We were cut off from the tallies during the crucial week leading up to the meeting," Waizenegger said.

It is unclear precisely why Broadridge stopped giving information to investors. The company told Reuters on Friday that the decision was not its own, and instead came from the Securities Industry and Financial Markets Association, a trade group whose members include JPMorgan.

On Saturday, SIFMA said that when it spoke to the company, Broadridge had already made up its mind to suspend passing along information. On Sunday, Broadridge said that the decision to stop passing along information was its own, and was based on its agreement with SIFMA that a broader review of the matter is warranted. On Monday, Broadridge said in a statement that it follows Securities and Exchange Commission regulations, and there are no rules requiring that voting information be provided to proponents of proxy measures.

Broadridge added, "given concerns raised by multiple broker clients regarding the release of this voting, we have stopped releasing voting information to proponents ..."

New York Attorney General Eric Schneiderman's office tried to learn on Thursday and Friday how a decision was made, according to a source familiar with the matter. Late Friday, Schneiderman's office sent a letter to JPMorgan's general counsel, Stephen Cutler, raising concerns about what had happened, the source said.

Staff from the Attorney General's office held two conference calls with JPMorgan on Saturday, and the bank agreed to tell Broadridge to provide interim results to the sponsors, the source said.

Broadridge then balked at providing the information, because it was not sure it had the legal authority to, the source said. But JPMorgan agreed to give the information directly to the sponsors as long as they signed a confidentiality agreement, the source added.

(Reporting by Dan Wilchins; Editing by Bernard Orr)