The several district courts of the United States are vested with jurisdiction specifically to enforce, and to prevent and restrain any person from violating any order or regulation made or issued pursuant to this chapter. Any civil action authorized to be brought under this chapter shall be referred to the Attorney General for appropriate action: Provided, That nothing in this chapter shall be construed as requiring the Secretary to refer to the Attorney General minor violations of this chapter whenever the Secretary believes that the administration and enforcement of the program would be adequately served by suitable written notice or warning to any person committing such violation.