Mark Lasswell is associate op-ed editor at The Post.

Any telling of the American labor story over the past half-century should be accompanied by a soft “fffttt” as the air leaks out of the union movement. Now, in the ultimate indignity, the National Labor Relations Board’s general counsel wants to stick a pin in Scabby the Rat.

About 30 years ago — the precise date is in dispute — unions in Chicago began accessorizing their protests with rodent inflatables they dubbed Scabby, an allusion to organized labor’s long-standing antipathy for workers who cross picket lines. The ratty mascots, ranging from human-size to two or three times that height, and afflicted with varying degrees of scabrousness, have become synonymous across the country with public displays of union outrage.

The giant rats may look like someone’s trying to appease the bubonic-plague gods, but Scabby’s presence outside a building or job site can lend a carnival-like air to an otherwise forlorn scene of grievance-harboring pipe fitters eating dank sandwiches out of Igloo coolers. The real attraction of the unattractive inflatable, though, is that you just know that his presence on the sidewalk is driving somebody upstairs in management nuts.

Late last year, one manager — in the form of the general counsel for the Republican-dominated NLRB board — finally couldn’t take it anymore and came storming out of the office to settle this balloon thing once and for all.

Peter B. Robb, who was appointed general counsel by President Trump in 2017 after a long career advocating for management in labor disputes, began issuing balloon-related memorandums and court filings with one thing in mind: rodenticide. He seemed intent on upending an Obama-era NLRB policy that treated Scabby’s personal appearances as a protected form of speech — a view reflected in rulings by courts and previous NLRB boards since the balloon’s debut three decades ago.

In recent months, Robb’s office has objected to inflatable rats outside supermarkets in Staten Island, N.Y., whose owner stoked the ire of a construction local that accused him of planning a new store in a shopping center built with non-union labor. Robb has also targeted the balloons near the entrance of a Philadelphia hotel that union electricians resented for using an electrical contractor that employed non-union workers.

Scabby the Rat’s inflatable pal, Fat Cat (which smokes a cigar and clutches a worker in its pillowy paw), prompted a memorandum from Robb’s office in December. The balloon had been deployed near a Chicago construction site to decry a contractor’s use of a non-union subcontractor at a different site.

Robb’s anti-rat-and-cat campaign is focused on that kind of “secondary” protest, when unions pursue a beef against a specific contractor by targeting neutral businesses that happen to employ the offending contractor. The magic word in the NLRB general counsel’s paperwork is “coercive” — the National Labor Relations Act blesses secondary protests as long as they don’t force customers or businesses to behave in a way that the union would find more appealing.

Scabby’s presence outside a workplace in the Philadelphia hotel scrape, Robb argued, was “confrontational, threatening and coercive.” (If he thinks the rat’s bad, he should take a look at the sinister Ronald McDonald and Pillsbury Doughboy balloons in the Macy’s Thanksgiving Day Parade.)

Robb’s efforts so far have been conducted in the realm of memos and lower-court skirmishes, but they could be a prelude to a formal NLRB ruling against Scabby, which would prompt a serious court fight over the First Amendment and labor rights — or at least as serious as a lawsuit involving balloons can be. The only development more gratifying than the current spectacle of a Trump appointee’s fury over a rat-shaped inflatable would be seeing the administration’s lawyers wrestling with Scabby in the Supreme Court.

If Scabby’s speech rights were restricted, it would be lamentable not only on First Amendment grounds but also on the grounds that unions have already suffered enough from self-inflicted wounds. And from federal anti-racketeering statutes.

Even the once-impregnable crony unionism of public-sector workers and their political patrons took a hit last year with a Supreme Court ruling that the employees no longer have to automatically cough up money to pay for unions’ collective bargaining. Overall, membership in organized labor in the United States hit a record low last year. There are few enough remaining unionized carpenters and joiners and electrical workers — let ’em trot out Scabby the Rat whenever they like.

Then again, the Trump administration’s battle might be just a rehearsal for an anti-inflatables campaign that has nothing to do with labor unions. Trump broke new diplomatic ground this summer, before American rapper A$AP Rocky’s assault conviction in Sweden, by pressing the Swedish prime minister to intervene in the case. How long until the president gets on the phone to Downing Street and asks Boris Johnson to do something about that big diapered “Trump Baby” balloon?

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