The Wagner Act was welcomed by the CIO for requiring employers to bargain collectively with the unions, although labour's so-called "bill of rights" was , as you note, hedged with bureaucratic restrictions embodied in the National Labour Relations Board which it created. AFAIK, Norris-Laguardia forbade yellow dog contracts and other forms of employer and court interference with unions and strike action, and the Wagner Act extended it to compel firms to enter into collective agreements with the unions, seen as necessary to restoring social peace. It was the Taft-Hartley Act in 1947 which required loyalty oaths and imposed the open shop and other reactionary provisions. But these are quibbles, and your comments underscore that where there is conflict over the scope of a reform, or where the corporations later want to weaken it when the relationship of forces has swung back in their favour, its interests will always be treated as paramount by the state - "the executive committee of the ruling class" whose autonomy from the latter is only relative and never absolute.
******* CB: Yes indeed. Historically, trade unions are inherently reformist organizations; not revolutionary. Engels has a group of journalistic essays on trade unions that sums up their political nature. In the period under discussion, trade unions were not Communist Parties.
Now today in the US, there is a social justice trend in US trade unions , especially with Trumka, that tends to seek to represent the working class as a whole rather than narrow trade unionism pure and simple , one's own shop floor. Representing and just thinking of the working class as a whole is a CP scope. ( See _Manifesto of the CP_. With the burst in working class consciousness from the Occupation's 99% vs 1% frame, US trade unions might transcend the traditional limitations. It is in their self-interest to reach out to the whole class. The Occupation gives them a party location to reach out to the class as a whole.
Also, the Occupation politicizes the Market, or _demonstrates_ to all the ruling class ruling through the state, the class nature of the state. Trade unionists actions are economistic and political ( See _What is to be done_) at the same time when they occupy wall street, monopoly capital. Lenin's riddle in What is to be done is solved in a new way.