In a city long teeming with rats, both literal and metaphorical, Scabby the Rat stood apart. The enormous balloon rodent loomed large on the streets of New York and across the country, with its buckteeth, menacing claws and crimson eyes drawing attention to the grievances of union protesters who had inflated it.

But after a set of recent memos and court filings from the National Labor Relations Board, some are worried that Scabby (and the rest of his anthropomorphic balloon menagerie) could soon be exterminated.

In documents filed in various cases around the country, the board has argued that the labor movement’s deployment of inflatable balloons like Scabby was unlawful.

The positions taken in the documents, which depict Scabby and others of that ilk as a disruptive form of illegal picketing, threaten the use of a powerful symbol that has helped union organizers draw attention to their campaigns against employers, labor leaders said.