Rep. Haley Stevens has pulled the plug on her support for Abdul El-Sayed ... announcing her endorsement of GOP candidate Mike Rogers for Michigan's senate seat.

Stevens, who was previously running against El-Sayed in the Democratic primary for Michigan's open Senate seat, has now thrown her support behind the Republican nominee ... rather than her fellow dem.

In a joint press conference with Rogers ... Stevens was heckled by someone calling her a "traitor" before the presser was abruptly ended.

Steven's fiancé Jason Turkish warned us on "TMZ Live" Friday that Haley might rescind her support for El-Sayed ... unless he openly condemned political ads she deemed to be anti-Semitic.

Feeling like she was no longer welcome on the El-Sayed campaign trail, Stevens says she woke up Sunday to give Rogers a heads up she would be heading to church and putting her support behind the Republican.

Just before she publicly endorsing Rogers ... Detroit News' Washington bureau chief Melissa Nann Burke reported that her "official staff including her longtime chief are resigning from her office this morning."

We've reached to Stevens' office for comment ... so far, no word back.