[4] The case was granted certiorari again to decide if the California court had jurisdiction to award damages arising out of peaceful union activity which it could not enjoin.

546, deserves repetition, because the considerations there outlined guide this day's decision: 'By the Taft-Hartley Act, Congress did not exhaust the full sweep of legislative power over industrial relations given by the Commerce Clause.

Congress formulated a code whereby it outlawed some aspects of labor activities and left others free for the operation of economic forces.

As to both categories, the areas that have been pre-empted by federal authority and thereby withdrawn from state power are not susceptible of delimitation by fixed metes and bounds.

But as the opinion in that case recalled, the Labor Management Relations Act 'leaves much to the states, though Congress has refrained from telling us how much.'

They regulate the vital, economic instruments of the strike and the picket line, and impinge on the clash of the still unsettled claims between employers and labor unions.

The extent to which the variegated laws of the several States are displaced by a single, uniform, national rule has been a matter of frequent and recurring concern.

[...] When it is clear or may fairly be assumed that the activities which a State purports to regulate are protected by § 7 of the National Labor Relations Act, or constitute an unfair labor practice under § 8, due regard for the federal enactment requires that state jurisdiction must yield.

Nor has it mattered whether the States have acted through laws of broad general application rather than laws specifically directed towards the governance of industrial relations.3 Regardless of the mode adopted, to allow the States to control conduct which is the subject of national regulation would create potential frustration of national purposes.

The adjudication in California has throughout been based on the assumption that the behavior of the petitioning unions constituted an unfair labor practice.

If the Board decides, subject to appropriate federal judicial review, that conduct is protected by § 7, or prohibited by § 8, then the matter is at an end, and the States are ousted of all jurisdiction.

The governing consideration is that to allow the States to control activities that are potentially subject to federal regulation involves too great a danger of conflict with national labor policy.