Chewing tobacco could be banned next year at AT&T Park. (Elsa/Getty Images)

Baseball’s long and ugly relationship with chewing tobacco could soon be coming to an end, at least in one major-league city.

San Francisco supervisors voted unanimously Tuesday to prohibit the use of smokeless tobacco at athletic venues, specifically mentioning baseball. It’s part of an initiative by the Campaign for Tobacco-Free Kids, which has targeted the city and state, and a broader bill, aimed at all tobacco use, is presently before the state Assembly.

It’s a trend that may be spiking as the dangers of smokeless tobacco are becoming increasingly well-known. Smokeless tobacco, like cigarettes, contains nicotine and that makes it addictive. It also raises the risk of cancer, heart disease and gum disease, among other ailments. “You can call chewing tobacco by whatever name you want — smokeless tobacco, spit tobacco, chew, snuff, pinch or dip — but don’t call it harmless,” the Mayo Clinic notes.

Hall of Famer Tony Gwynn, who died last June, believed that his lengthy habit of using smokeless tobacco was to blame for his cancer of the mouth and salivary glands. Gwynn, whose career spanned 20 years, played at a time when baseball players typically sported a cheek bulging with tobacco, spitting a black stream of juice during games and in the dugouts. There was no doubt in his mind that the disease caused him to require two lengthy surgeries in an attempt to arrest the cancer.

“Of course, it caused it,” Gwynn said. “I always dipped on my right side.”

Tony Gwynn Jr. made a strong case against dipping in an interview on HBO’s “Real Sports” on Tuesday night.

More players, like Stephen Strasburg of the Washington Nationals, are quitting the habit, which is banned in the minor leagues, but the Major League Baseball Players Association is an odd and formidable opponent. Since the 2011 collective bargaining agreement, MLB has prohibited teams from providing tobacco products to players and encourages clubhouse attendants not to get them for players. Players are not allowed to have tobacco tins in the pockets of their uniforms (no more of those telltale round impressions). Players cannot do TV interviews while using smokeless tobacco and violators of any of these rules can be fined.

However, smokeless tobacco remains a negotiable contract issue between MLB and the MLBPA.

The ordinance will require a formal vote by the board next week and would go into effect Jan. 1. At AT&T Park, signs would be posted and violators ejected. “We would hope it doesn’t come to that,” Jess Montejano, an aide to Supervisor Mark Farrell, told the Associated Press, “and that the league would work to educate players coming to AT&T Park.”