Blake Lively's 'Sisterhood Of the Traveling Pants' Costars Blast Alleged Smear Campaign

Blake Lively is receiving support from some of her oldest costars and friends ... America Ferrera, Amber Tamblyn and Alexis Bledel have issued a statement amid her "It Ends With Us" lawsuit.

The 3 actresses -- all of whom starred in the "Sisterhood of the Traveling Pants" film franchise with Blake in the '00s and have remained her good friends -- issued a joint statement on Instagram ... where they made it clear they were standing behind BL amid her legal battle.

They wrote ... "Throughout the filming of 'It Ends with Us,' we saw her summon the courage to ask for a safe workplace for herself and colleagues on set and we are appalled to read the evidence of a premeditated and vindictive effort that ensued to discredit her voice."

As the women continued, they noted that they were upset to see "the unabashed exploitation of domestic violence survivors' stories to silence a woman who asked for safety" ... and noted that the "hypocrisy was astounding."

Before they signed off their statement, they praised Blake for speaking out, adding ... "We are struck by the reality that even if a woman is as strong, celebrated, and resourced as our friend Blake, she can face forceful retaliation for daring to ask for a safe working environment."

TMZ broke the story ... Blake sued "It Ends With Us" director and costar Justin Baldoni, in which she alleged a smear campaign was conducted against her after she accused him of sexual harassment while filming the drama.

Baldoni's lawyer, Bryan Freedman, later slammed the lawsuit ... calling it an attempt to "fix her negative reputation."