update

2:27 PM PT -- Sources with direct knowledge tell TMZ ... The Micheal Jackson estate hasn't tried to shutdown "MJ Live" during its run in Nevada due to state laws protecting impersonator shows. However, Michael's estate is now taking action because they view the show as low class and don't want it running in states like California, New York and others. Plus, the estate is already behind "MJ: The Musical" which is currently on Broadway.

A tribute show in Las Vegas says the late singer's estate is trying to shut down their show .

.. and now they're duking it out in court.

According to new legal docs, obtained by TMZ, the folks behind the "MJ Live" show at the Tropicana claim the Michael Jackson estate recently began sending cease and desist letters threatening them with legal action over the show, claiming it's using the estate's trademarks without permission.

Thing is ... "MJ Live" claims they've been doing their thing for well over a decade -- performing for over 2.5 million people -- and the estate has only recently started making legal threats.

In other words, they're suggesting this came out of nowhere ... unjustly.

In the docs, "MJ Live" says the act is going on the road and Michael's estate is trying to shut down shows scheduled at venues in California, Florida, Illinois, Ohio, and Wisconsin.

Meanwhile, the tribute show points out the estate is starting up a tour of its new Broadway show, "MJ: The Musical" ... suggesting the timing of the legal beef may be related to the estate trying to cash in with their own MJ show.

They even go so far as to claim that the MJ estate is actually the one infringing on their own intellectual property with "MJ: the Musical" .

.. basically arguing, they were their first doing their own thing -- and that their brand as "MJ Live" has established its own reputation/brand.

Anyway, the "MJ Live" producers want a judge to declare that the art they use to promote their show doesn't infringe on the estate's trademarks because their artwork is distinct and causes no confusion to the public.

A rep for MJ's estate tells TMZ, "This lawsuit -- including the claim that this impersonator show somehow owns a ‘trademark’ in ‘MJ,’ a trademark owned by Michael Jackson’s Estate and long associated with Michael and his Estate -- is beyond frivolous.

The Estate, as always, will vigorously defend all intellectual property rights of Michael Jackson."