Two powerful union leaders are demanding that Rep. Richard Gephardt (D-Mo.) fire one of his top aides after she allegedly threatened to retaliate against their unions if they campaign for former Vermont Gov. Howard Dean in Missouri.

In a letter sent to Gephardt today, Andrew Stern and Gerald McEntee allege that Gephardt’s presidential campaign vice chairwoman, Joyce Aboussie, issued an ultimatum Monday: that any campaign activity on behalf of Dean in Missouri would result in Gephardt seeking to strip collective bargaining authority from unionized Missouri state workers. Stern and McEntee, heads of the Service Employees International Union and American Federation of State, County and Municipal Employees, respectively, both recently endorsed Dean in what was seen as a major blow to the Gephardt campaign.

“It’s bad enough to deliver an ultimatum to any group of people,” McEntee and Stern wrote. “But for a senior aide of yours … to do so at the expense of Missouri’s state employees is deplorable.”

The letter added: “This was an unconscionable act. You should disassociate yourself from Ms. Aboussie, immediately remove her from your campaign and issue a written retraction of her threats.”

The Gephardt campaign did not deny that Aboussie had made the threat.

Gephardt campaign manager Steve Murphy said the Congressman “strongly supports collective bargaining rights for public employees in Missouri and throughout the country and he strongly supported the collective bargaining executive order issued by Gov. Holden.”

The letter shows the increasing depth of animosity between the Gephardt and Dean camps as they battle for the Democratic presidential nomination. The two are running neck-and-neck in the Jan. 19 Iowa caucuses and will face off again two weeks later in the Missouri primary. Gephardt, of course, is heavily favored to win his home state.

According to McEntee and Stern, during a Dec. 1 meeting with Missouri Gov. Bob Holden (D), his top aide and representatives from AFSCME and SEIU, Aboussie allegedly threatened to send a letter to top GOP state legislators asking them to overturn an executive order by Holden granting collective bargaining to unions representing Missouri state employees.

Holden is facing a serious primary challenge from state Auditor Claire McCaskill next year.

Aboussie is often described as the head of Gephardt’s political operation and has worked for him since he was first elected to Congress in 1976. So far, Aboussie has raised more than $4 million herself for her boss’s 2004 White House bid.