def validate_resiliencypolicy_tier(tier):
    """
    Validate Type for Tier
    Property: ResiliencyPolicy.Tier
    """

    VALID_TIER_VALUES = (
        "MissionCritical",
        "Critical",
        "Important",
        "CoreServices",
        "NonCritical",
    )

    if tier not in VALID_TIER_VALUES:
        tier_values = ", ".join(VALID_TIER_VALUES)
        raise ValueError(f"Tier must be one of {tier_values}")

    return tier