Michael Lohan's Ultimatum to Lindsay

Lindsday Lohan's dad tells TMZ he will back off trying to get his daughter placed in a conservatorship if ... and only if ... she agrees to a sit down, and stat.

Michael Lohan says he wants a meeting with Lindsay and her lil' sis Ali ... no Dina, no lawyers, just his daughters.

Michael says if they agree, he won't go to the L.A. County Department of Children and Family Services and ask that Ali be removed from Lindsay's home. Michael said during TMZ Live yesterday he believed Ali was in danger by living with her older sister.

And, although Michael told us during TMZ Live he would ask a judge to place Lindsay under a conservatorship ... he now says he won't make that move either if Lindsay sits down with him.

One little stumbling block ... Lindsay isn't listening to anyone these days, and she's been Tweeting up a storm about how she blames her dad for everything bad in her life.