diff --git a/backend/alembic/versions/e1f2a3b4c5d6_seed_sectors_for_existing_companies.py b/backend/alembic/versions/e1f2a3b4c5d6_seed_sectors_for_existing_companies.py
new file mode 100644
index 00000000..1fee5b1b
--- /dev/null
+++ b/backend/alembic/versions/e1f2a3b4c5d6_seed_sectors_for_existing_companies.py
@@ -0,0 +1,63 @@
+"""seed sectors for existing companies
+
+Siembra el catálogo de sectores PROSEC (a76.sectors) para todas las empresas
+existentes. Los sectores son por empresa y solo se sembraban dentro de
+_seed_company_data() al crear una empresa; las empresas que no pasaron por ese
+flujo (BD recreada o creadas por otra vía) quedaban sin sectores y el selector
+del frontend aparecía vacío. Idempotente: ON CONFLICT DO NOTHING.
+
+Revision ID: e1f2a3b4c5d6
+Revises: c8d9e0f1a2b3
+Create Date: 2026-06-02 14:00:00.000000
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+from sqlalchemy import text
+from sqlalchemy.orm import Session
+
+from api.v1.modules.a76.general_catalogs.sectors.seed import seed as sectors_seed
+
+revision: str = "e1f2a3b4c5d6"
+down_revision: Union[str, None] = "c8d9e0f1a2b3"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    def format_value(val):
+        if val is None or str(val).strip() == "" or str(val).upper() == "NONE":
+            return "NULL"
+        return f"'{str(val).replace(chr(39), chr(39) * 2)}'"
+
+    bind = op.get_bind()
+    session = Session(bind=bind)
+    companies = session.execute(
+        text("SELECT tenant_id, id FROM a76.company WHERE deleted_at IS NULL")
+    ).fetchall()
+
+    for tenant_id, company_id in companies:
+        values = ", ".join(
+            [
+                f"({format_value(key)}, {format_value(description)}, {str(authorized).upper()}, {tenant_id}, {company_id})"
+                for key, description, authorized in sectors_seed
+            ]
+        )
+        if values:
+            session.execute(
+                text(
+                    f"""
+                    INSERT INTO a76.sectors (key, description, authorized, tenant_id, company_id)
+                    VALUES {values}
+                    ON CONFLICT (key, tenant_id, company_id) DO NOTHING;
+                    """
+                )
+            )
+    session.commit()
+
+
+def downgrade() -> None:
+    # Backfill de datos: no se eliminan sectores en el downgrade porque podrían
+    # haberse editado/agregado manualmente tras la siembra. No-op intencional.
+    pass