Taser International, the stun-gun maker emerging as a leading supplier of police body cameras, has cultivated financial ties to police chiefs whose departments have bought the recording devices, raising conflict-of-interest questions.

Taser is covering airfare and hotels for police chiefs who speak at promotional conferences and is hiring recently retired chiefs as consultants, sometimes months after their cities signed contracts with the company. Taser is planning to send two to speak in Australia and the United Arab Emirates in March at events during which they will address potential customers.

The relationships raise questions about whether chiefs are acting objectively in their dealings with Taser, whose contracts for cameras and video storage can cost millions.

As the police chief in Fort Worth, Texas, pushed for signing a contract with Taser before a company quarterly sales deadline, he wrote a Taser representative in an email, "Someone should give me a raise."

The market for wearable cameras for police that can record arrests and shootings has been growing fast since the killing last August of 18-year-old Michael Brown by an officer in Ferguson, Missouri. Supporters say the cameras reduce tensions between officers and the communities they serve.

City officials and rival companies are raising concerns about police chiefs' ties to Taser as it profits from the boom.

"Department heads need to be very careful to avoid that type of appearance of an endorsement in a for-profit setting," said Salt Lake City councilman Charlie Luke.

He said he was surprised when he learned last year that the city's police department had purchased Taser cameras using surplus money, bypassing the standard bidding process and City Council approval.

The department declined to say how much it has spent acquiring 295 body cameras and Taser's Evidence.com video storage program and has not responded to a month-old public records request.

The city's police chief, Chris Burbank, said that his relationship with Taser is appropriate but understands how others might see favouritism. He recently recorded a company promotional video in which he praised Evidence.com.

Burbank said he does not receive speaking fees and believes he hasn't violated a city code prohibiting paid product endorsements on public time. He said he accepts Taser's speaking invitations to promote best practices for body cameras.

A Taser spokesman said the company has no control over how cities decide to award contracts and that its products have unique features. Taser says early adopters of technology are the best ones to discuss its benefits and share their experiences with colleagues.

"This is a pretty normal practice for police chiefs and other recently retired individuals to speak on behalf of the industry," Taser spokesman Luke Larson said.

Taser's competitors complain they have been shut out by cities awarding no-bid contracts and sometimes feel disadvantaged when allowed to compete.

"Every time I do a presentation, as I'm standing there looking through the room, I wonder, 'Who is tainted by Taser?"' said Peter Onruang, president of Wolfcom Enterprises, a California body camera maker.

Taser's relationship with the chief in Albuquerque, New Mexico, prompted an investigation by the city's inspector general.

City Council members demanded the inquiry after learning that Chief Ray Schultz, who supported the $1.9 million contract, became a company consultant after stepping down. A U.S. Justice Department investigation criticized Albuquerque's rollout of the body cameras, saying it had been too hasty.

Today, Schultz speaks in an online promotional video about Albuquerque's experience with Evidence.com. Although he's recently been hired as assistant chief in the Houston suburb of Memorial Villages, Schultz said he will be paid by Taser to speak at the international conferences in March.

Former New Orleans Police Superintendent Ronal Serpas confirmed he signed a Taser consulting agreement after his August retirement and has spoken at company-sponsored events. Serpas said it did not violate a state ethics law because he's not lobbying his former employer, adding he wasn't on the committee that recommended Taser for a $1.4 million contract.

In Fort Worth, then-Police Chief Jeffrey Halstead was seeking 400 more body cameras for officers last year. Taser promised a discount if the deal could be approved before the end of the company's sales quarter, emails show.

Over the next three weeks, Halstead pushed the city to approve a no-bid contract worth up to $2.7 million. In the following months, Taser had Halstead speak at events in cities such as Phoenix, Miami and Boston.

Halstead, who retired from Fort Worth in January, said he hopes to become a Taser consultant soon.

Associated Press writers Brian Bakst in St. Paul, Minnesota, and Don Thompson in Sacramento, California, contributed to this report.