Obama clinched the Democratic Party's nomination on June 3.
Jonathan Mantz, Clinton's national finance director, notified donors about the meeting by e-mail Tuesday and urged them to attend.
Two people closely involved with Clinton's fundraising said the meeting had taken on added urgency after several of her money "bundlers" complained that Obama campaign manager David Plouffe and others had come across as arrogant in meetings with them last week in New York and Washington.
Both individuals spoke on condition of anonymity because they were not authorized to speak publicly about the meeting.
Among other things, the donors want to make sure Obama knows that in order to get their help he needs to help Clinton pay down her campaign debt.
The two fundraisers who discussed the meeting said many donors also are furious that Obama's campaign hired Patti Solis Doyle as chief of staff to Obama's eventual running mate, calling it a slap in the face to Clinton and an implicit acknowledgment that she would not be on the ticket with him.
Obama spokesman Bill Burton said no inference about the selection of a running mate should be made from Solis Doyle's hiring.
"This was a long and hotly contested fight, so obviously there are some strong feelings about how it turned out and what needs to happen moving forward," he said. "But we're confident that the Democrats are united in their desire to defeat (Republican) John McCain."
Clinton and Obama will meet with two different groups of donors at the Mayflower a week from Thursday. One larger group will include donors who raised $250,000 for Clinton's campaign. A more intimate session will be reserved for about 30 fundraisers who collected $1 million or more.
"The challenge is reaching out to donors to ask them for money for a candidate that they've been on the opposite side of for a year and a half," said Alexander Heckler, Clinton's Florida finance chairman. "However, we have to take a deep breath and realize that we need to all work together and have a Democratic president elected."
Another Clinton fundraiser suggested there was no rift, noting that a vigorous primary contest had just ended.
"The Obama campaign has reached out to the Clinton people," said Hassan Nemazee, Clinton's national finance co-chairman. "I think this is a process that is being undertaken and hopefully we will be in a position to assimilate the Clinton fundraising operation and the Obama fundraising operation together in the near future."
"The reality is that we're two weeks from the day that the last primary was held," he added. "It takes a little while for staff to talk to each other, for lay organizations to talk to one another. It's taken a while to get the candidates available."
Heckler said he has been working with Obama's camp and said he and Obama's Florida finance chairman, Kirk Wagar, have been speaking daily to discuss fundraising strategies.
--- Beth Fouhy reported from New York.
