Is the other shoe about to drop for Crocs?

Crocs' feet are being held to the fire. 

The U.S. Patent and Trademark Office (USPTO) has ruled that the design patent for the shoe maker's famous molded plastic clogs is invalid, according to Footwear News. The decision was lauded by rival U.S.A. Dawgs, which had challenged the patent and is also embroiled in legal fights with Crocs (CROX) over advertising complaints and alleged corporate sabotage.  

The decision comes at a sensitive time for Crocs, which told Footwear News it plans to challenge the ruling. The company is trying to get lighter on its feet by refreshing its lineup of clogs and sandals, but revenue slipped almost 3 percent in the most recent quarter. With fewer people slipping into its iconic shoes, the company is planning on closing about 160 retail locations. 

The patent issue has been pending for several years after U.S.A. Dawgs challenged its validity. 

"It is unfortunate that Crocs has been able to use this patent to suppress its competitors for so long," said Dawgs CEO Steven Mann, in a statement. "We have always been confident that, given a fair playing field, Dawgs would become a prominent competitor."

Fashion attorney Elizabeth Kurpis told Footwear News the USPTO ruled the design invalid "because the shoe design could be 'anticipated' from prior similar shoe designs." 

A bigger question may be what's left to fight over. The retail sector has become increasingly challenging, with stores such as Gymboree and Bebe running into financial troubles as consumers increasingly flock to online rivals. 

Consumers also appear less interested in the funky plastic clogs, which might best be known as the favored footwear of celebrity chef Mario Batali. Sales aren't going to revive anytime soon for Crocs, which on Thursday said it expects lower revenue this year, partly due to store closings.