Fitbit Flex measures and records your physical activity and, combined with a website and a smartphone app, is a formidable lifestyle tracker.

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A DISPUTE between two leading makers of wearable devices escalated after Jawbone accused larger rival Fitbit of violating federal antitrust laws and Fitbit sued to block imports of some Jawbone products.

Fitbit on Monday filed a complaint with the International Trade Commission to halt US imports of Jawbone products that allegedly infringe on Fitbit patents, according to a securities filing.

Jawbone had earlier asked the trade commission to block Fitbit imports.

Jawbone, incorporated as AliphCom, said Fitbit’s complaint "underscores its anticompetitive conduct in the marketplace".

Jawbone filed an antitrust claim on Friday in US District Court in San Francisco, in response to a patent lawsuit from Fitbit.

In the filing, Jawbone accuses Fitbit of poaching its employees, stealing trade secrets and filing "meritless" patent lawsuits that are "part of its by-any-means-necessary campaign to impede competitors and preserve its dominant position in the fitness-tracker market".

Fitbit called the allegations "unfounded, and yet another misguided attempt for publicity to deflect attention from Jawbone’s own lack of performance".

Late on Monday Fitbit said its third-quarter profit fell by a third to $45.8m from a year earlier, in part because of one-time benefits last year.

Its revenue nearly tripled to $409m in the quarter.

The two San Francisco-based companies sell wearable fitness trackers for users’ wrists and clothing that monitor wearers’ activity.

The devices are a fast-growing sector of consumer electronics, with more than 21-million sold last year, more than three times as many as in 2013, according to legal documents.

Both Jawbone and Fitbit face new competition from Apple’s Apple Watch.

Jawbone has shown signs of financial strain.

A supplier last year briefly sued the company for more than $20m in late payments and said Jawbone’s "financial condition is perilous".

Jawbone recently borrowed $300m from money manager BlackRock.

Fitbit, which went public in June, has said it controls 85% of the fitness tracker market, and expects to post about $1.8bn in revenue this year.

Jawbone says it is the market’s number two player.

Jawbone’s antitrust claim relies in part on prior accusations that Fitbit hired Jawbone employees to steal trade secrets.

In Friday’s filing, Jawbone said Fitbit earlier this year implemented a plan to "decimate Jawbone by hiring away key employees and stealing trade secrets".

Jawbone said Fitbit contacted an estimated 30% of Jawbone’s 400 workers and ultimately hired five, who then allegedly took 18,000 of Jawbone’s confidential digital files to Fitbit.

The allegedly transferred files included documents on the company’s financials, market research and diagrams of an unreleased fitness headset.

A California Superior Court judge last month issued a preliminary injunction in the case and ordered the Fitbit employees to return the files.

Jawbone said the employees had returned copies of the files but not the originals.

Jawbone is also asking the International Trade Commission to block Fitbit from importing virtually all of its products into the US because of the alleged theft of trade secrets.

A hearing is scheduled for May 2016 in that case.

Fitbit and Jawbone are also suing each other over the technology underpinning their devices.

Jawbone sued Fitbit for patent infringement in federal court in San Francisco in June.

Fitbit has sued Jawbone three times in the past two months, in federal courts in San Francisco and Wilmington, Delaware, for allegedly infringing nine Fitbit patents covering how fitness trackers connect with smartphones and how they notify users when they meet fitness goals, among other things.

Fitbit said separately on Monday that it planned a follow-on equity offering of 7-million shares to raise more money, while certain stockholders would sell another 14-million shares.

The news sent Fitbit shares down 7.1% to $37.89 in after-hours trading.

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