Sales of medium- and heavy-duty trucks in the U.S. slipped 0.9% last month, tallying 28,766 units, WardsAuto data shows.

The flat month saw modest increases in most groups, despite a sales slowdown virtually across the board for troubled International.

International’s woes had an acute impact on industry Class 8 deliveries, which fell 10.7%. The Illinois-based truck maker saw the heftiest drop, down 35.2% to 2,758 units.

A handful of other mid-volume players lost ground in the sector, as well, including PACCAR’s Peterbilt, sales of which slid 15.8%.

Daimler’s Western Star records the biggest increase among heavy-duty makers, with deliveries up 33.7% on 242 units.

International also posts the biggest drop in Class 7, at 25.4%, and remains in second place in the segment for the year. It led Class 7 sales in calendar 2011.

UD Trucks’ 229.6% jump on modest volume of 89 units, vs. 27 year-ago, represents Class 7’s largest increase.

UD Trucks also led all gainers in Class 6, which rose 2.8% overall. The truck maker saw sales skyrocket 635.7%, as it took a 5.9% segment share in the month, up from 0.8% year-ago.

Ford posts a triple-digit percentage increase in Class 6, up 134.9%.

International, last year’s No.1 Class-6 seller, suffers a 32.3% drop in sales compared with like-2011, the segment’s biggest decline.

Class 5’s 30.0% increase was the largest of any group last month, driven by a 54.8% surge in demand for segment-leading Ford. A 57.0% decline for International ate away at some of the gain provided by Ford.

Contrary to its performance in other groups, International climbed sharply in Class 4, up 473.8% in October, selling a segment-leading 350 units.

However, International’s strong showing wasn’t enough to offset losses by most other manufacturers, including Ford, which tumbled 95.6% on modest volume, and Daimler, plunging 70.2% to 85 units.

Despite the sales slowdown in recent months, medium- and heavy-duty trucks were tracking 17.1% ahead of year-ago through October, to 288,265 units.

Stocks rose at the end of last month, with Class 8 days’ supply reaching 65 on 38,771 vehicles, up from year-ago’s 49 days and 32,648 units.

Inventories were higher for medium-duty models, at 79 days, or 40,107 units, compared with 74 days, or 33,268 vehicles, in late October 2011.

In other big-truck news, the Canadian Auto Workers’ union is angry over International-maker Navistar’s move this week to ask a Windsor, ON, court to dismiss a lawsuit filed by former workers who claim they are owed severance as a result of a factory closing more than a year ago.

The workers were employed at Navistar’s Chatham, ON, plant, which halted production in June 2009 before closing for good in August 2011.

“Every step of the way, Navistar has tried to block handing over what is owed to its former workers – it is deplorable and should not be allowed to continue,” CAW President Ken Lewenza says in a statement.

Navistar lawyers claim the court isn’t authorized to hear the class-action lawsuit, which they say falls under the jurisdiction of the Ontario Labour Relations Board.

The two sides have been trying to forge a settlement for two years, reports The Windsor Star.

The case has been adjourned until Nov. 21 or 22, the newspaper says.

Navistar has been in headline-making mode in recent weeks as it works to restructure under interim CEO Lewis Campbell.

The truck maker announced Oct. 30 it will close its Garland, TX, truck plant, displacing 900 workers, and shifting production in January to operations in Escobedo, Mexico, and Springfield, OH. Closing the Garland plant should result in annual savings of $25 million-$35 million, Navistar says.

Earlier this month, Navistar raised $14 million-plus through the sale of more than 700,000 shares, priced at $18.75 per share.