Even as they look for a new home in Oakland, the A’s are erecting a party deck in the Coliseum’s left field stands — looking to add a bit of pizzazz to the old stadium in hopes of drawing more fans.

But their stadium mates, the short-timer Raiders, are not happy about it.

The Treehouse, as the party deck has been branded by the A’s, extends off the club level to the east side of the stadium. It takes up 10,000 square feet and features a redwood patio, a bar and lounge seating.

The $1 million structure is modeled after party decks at Coors Field in Denver and Great American Ball Park in Cincinnati. The deck will double as a setting for pre- and post-game TV and radio broadcasts. It will also feature a DJ on Friday nights.

Team President Dave Kaval said the deck was part of a strategy to offer “dynamic and new ways to enjoy A’s baseball.” The hope is that the laid-back seating will attract younger fans looking for a casual environment from which to take in the game.

The team could use some help in attracting those fans. Last season, the A’s came in next to last in Major League Baseball attendance (just ahead of Tampa Bay), averaging crowds of 18,219.

By comparison, the Giants drew an average of 40,786 fans per game.

Putting in the Treehouse, however, also means tearing out 300 seats to make way for three long rows of “drink rails” where standing fans can park their beers. And that’s where the Raiders’ problem comes in — the team has already sold those seats to season ticket holders.

Coliseum officials said the rails could be removable and the seats could be replaced with cushioned chairs for football games.

Not good enough, said the Raiders, who said the changes violated their lease deal and would cause them “material damage.”

Insiders say the real play here is that the Raiders are trying to gain leverage in lease extension talks that will cover their remaining years in Oakland until their Las Vegas stadium is built.

The Oakland-Alameda County Coliseum Authority, which still has nearly $80 million in debt from the 1990s renovation that lured the Raiders back from Los Angeles, wants the extension at least to break even for taxpayers.

A Coliseum Authority audit in April showed that the Raiders owed the city and county $800,000 in parking revenue dating back five years — a figure the team has disputed.

Plus, under the Raiders’ current lease, the authority claims to be losing about $1.5 million a year from game-day expenses, such as providing security, ushers and parking attendants — as well as from the cost to convert the Coliseum from baseball to football use.

As for whether the Raiders will cover the losses, authority Executive Director Scott McKibben said, “We are in the talking stage, and they have our proposal in hand.” He declined to provide details.

The Raiders did not return our call seeking comment.

In the meantime, the A’s say their party deck will be ready for Opening Day on March 29.

Name game: San Francisco mayoral candidate Mark Leno’s campaign headed to court Tuesday in an effort to strip “acting mayor” from Supervisor London Breed’s job description on the June ballot.

“Supervisor Breed’s current ballot designation is factually inaccurate and misleading ” Leno said as his lawyers put the finishing touches on a petition to Superior Court, asking a judge to order the change.

“Voters deserve the truth,” Leno said.

“To be clear — this is not board President Breed’s call,” said Breed campaign spokeswoman Tara Moriarty. “It’s up to the Department of Elections to defend its decision on the ballot designation.”

Elections Department Director John Arntz said he had not seen Leno’s petition.

Under San Francisco election rules, the job a candidate holds on the day of the filing deadline is the job that is listed on the upcoming ballot.

Leno is a former supervisor, state assemblyman and state senator — all titles that convey experience in government. On the ballot, however, Leno can only use his current job title — “small businessman” — because he wasn’t in office on the day of the filing deadline, Jan. 9.

In Breed’s case, she was both “acting mayor” following the death of Mayor Ed Lee and a supervisor when deadline day came.

Breed’s camp wanted her ballot designation to be “acting mayor,” with no reference to her lesser position as a supervisor.

After a bit of back and forth with the Department of Elections, it was agreed that Breed would have the twin designation — “acting mayor/supervisor”— next to her name.

Two weeks later, Breed’s tenure as acting mayor ended when six of her colleagues chose Mark Farrell to be mayor until June.

However, Breed’s mayoral exit occurred after the 10-day period during which her ballot designation could be contested. The only recourse for those unhappy with Breeds’ “acting mayor” title was the courts.