I'm only aware of a few mysteries set during the Labor Day Holiday: Lee Harris's Labor Day Murder, Sharyn McCrumb's Highland Laddie Gone, Sandra Balzo's Running on Empty, and Mary Jane Maffini's The Devil's in the Details (Labour Day Weekend-Canada). There's also the short story "Labor Day" by R.T. Lawton in Alfred Hitchcock Mystery Magazine.
Labor Unions, on the other hand, are rife with settings and situations for crime fiction. This is an UPDATED Crime Fiction list involving Labor Unions with links to two great articles. Please let me know any books that are missing from this list.
LABOR UNION CRIME FICTION
The Knife Behind You by James Benet (Department Store Union Organizer)
For the Love of Mike by Rhys Bowen (Garment Workers Union)
White Hot by Sandra Brown (Labor Dispute)
Big Boned by Meg Cabot (Graduate Student Union)
Double Indemnity by James M. Cain (Insurance)
All Men Fear Me by Donis Casey (IWW)
Cactus Blood by Lucha Corpi (Farm Workers' Union)
Airframe by Michael Crichton (Union Trouble)
Red Herring by Jonothan Cullinane (Waterfront Strike)- coming out this Fall
The Valley of Fear by Arthur Conan Doyle (Union Group called the Scowrers)
Third Strike by Philip Craig and William Tapply (Steamship Authority Strike)
October Heat by Gordon DeMarco (1934 San Francisco General Strike-Longshoremen)
Valley of Fear by Arthur Conan Doyle (The Scowrers)
The Bramble Bush (aka Worse than Murder) by David Duncan (San Francisco General Strike)
American Tabloid by James Ellroy (Teamsters)
LA Quartet by James Ellroy (Movie Unions)
A Place Called Freedom by Ken Follett (Coal Mines)
The Peripheral Son by Dorien Gray
Dead Reckoning by Patricia Hall (Union Strike)
Red Harvest by Dashiell Hammett (IWW organizer & Copper Workers; Strike Breaking)
A More Perfect Union by J.A. Jance (Iron Workers' Union)
As Dead As it Gets by Cady Kalian (Creative Artists' Union)
The Longer the Thread by Emma Lathen (Garment Workers)
Death at the Old Hotel by Con Lehane (Hotel Workers' Union)
Through a Glass Darkly by Donna Leon (not a union exactly but unsafe working conditions and pollution in the Venetian glass industry)
The Given Day by Dennis Lehane (Police Union)
Through a Glass Darkly by Donna Leon (Unsafe environmental pollution in Venetian glass factories effecting workers)
Black Water Rising by Attica Locke (Long Shoremen's Union)
Deadly Dues by Lulu Malone (Actors' Union)
Stiff by Shane Maloney (Meat Packing)
Lorraine Connection by Dominique Manotti (Union rep in Cathode-ray Tube industry)
Champawat by Lia Matera A Novella in Ellery Queen Mystery Magazine (Labor Unions & the Clash between Anarchists & Democrats)
Organize or Die by Laura McClure (Union organizing)
Conferences are Murder by Val McDermid (Journalists' Union)
Death at Pullman by Frances McNamara (American Railway Union)
The Viewless Winds by Murray Morgan (Murder of a Labor Leader's wife)
A Red Death by Walter Mosley (Aircraft Manufacturer and Labor Union organizer)
Blanche on the Lam by Barbara Neely (Domestic Workers)
Indemnity Only by Sara Paretsky
Mr Campion's Fault by Mike Ripley (Mineworkers)
Death and Blintzes by Dorothy and Sidney Rosen (Garment Workers Union)
A Bitter Feast by S. J. Rozan (Restaurant Workers' Union)
Some Cuts Never Heal by Timothy Sheard (Shop Steward)
Judas Incorporated by "Kurt Steel" (Rudolf Kagey) (Pro-Union)
The Big Both Ways by John Straley (Lumber)
The Labor Union Murder aka Fourth of July Picnic by Rex Stout (novella)
Absolute Rage by Robert K. Tanenbaum (Coal Miners' Union)
Fallout by Paul Thomas
The Porkchoppers, Yellow Dog Contract by Ross Thomas (Politics & Unions)
Killy by Donald Westlake (Manufacturing Union)
For further reading:
The Strange Connection Between Detective Fiction and Union Busting by Erica Eisen
Radical Noir: 26 Activist Crime Novels by Molly Odintz
Have a great Labor Day Holiday!
