Reps. Eric Swalwell and Charlie Crist fired off a letter to Spears, asking her and her attorney, Mathew Rosengart, to explain "how you achieved justice..." The 2 congressmen wrote, "There is no doubt your story will empower countless others outside the millions that are already inspired by you and your art."

The 2 Congressmen say they want to learn "about the emotional and financial turmoil you faced within the conservatorship system." The letter goes on to say they are concerned that Britney was "forced to engage in employment against your will."

The Congressmen make it clear in the letter ... they're fully on board the #FreeBritney movement, saying, "We applaud your inspiring fight and stand ready to assist in any way we can."

For her part, Britney said she was grateful ... "I felt heard and like I mattered for the first time in my life !!!" She got the letter in December, but said she wasn't nearly at the healing stage she's in now.

Rep. Crist appeared on TMZ Live today to talk about the invite.