San Francisco Supervisors Aaron Peskin and Hillary Ronen are calling for the city to boycott any business that helps build President Trump’s wall along the Mexican border.

“It’s important for people to stand up in every conceivable way, and if that happened — including in (pre-World War II) Germany — the world may have been a different place,” Peskin said.

Ronen said she got the idea from a Bernal Heights resident she met during her supervisorial campaign last year. “I don’t want corporations profiting off human rights abuses at the border and our city participating in that,” she said.

The legislation she and Peskin are floating would prohibit the city from doing business with any company that receives a contract to “participate in any way” in constructing the wall.

It’s more than a symbolic protest, they say.

“San Francisco works with all the major construction firms in America — in fact, we are putting the finishing touches on an over $2 billion transbay terminal involving hundreds of companies,” Peskin said. “And if other cities and states that spend billions on public works projects start adopting similar measures, then it sends a powerful message.”

San Francisco political leaders have long used the threat of pulling city contracts to make a political point or right the world’s wrongs.

Most recently, Mayor Ed Lee banned all nonessential city-employee travel to North Carolina to protest a law in that state that opponents said discriminated against the LGBT community.

The mayor ordered a similar ban when then-Gov. Mike Pence of Indiana signed a religious freedom bill that many also viewed as discriminatory against gays and lesbians. Pence later put his signature on an amended bill passed by the Indiana Legislature, and the travel ban was lifted.

And in 2010, then-Mayor Gavin Newsom ordered a moratorium on city-employee travel to Arizona — and tried to extricate the city from any Arizona-related contracts — in response to an anti-immigration measure in that state.

Some actions have been far-reaching.

In 1978, San Francisco became one of the first cities to pass legislation barring investment in companies doing business in or with South Africa — a campaign that eventually spread to the federal government and within a decade led to the dismantling of South Africa’s apartheid system.

And in 1996, San Francisco supervisors passed the first equal benefits ordinance — a move that forced United Airlines, based at SFO, to provide equal benefits to gay and lesbian couples, and eventually led all airlines to follow suit.

Other efforts have had unexpected consequences.

A 2005 ban on sweatshop products, for example, became so burdensome for companies to comply with that they simply stopped bidding for city contracts. At one point the city was unable to keep up with police demand for bullet-resistant vests.

Early warning: If San Francisco Mayor Ed Lee and other Bay Area officials were surprised by President Trump’s executive order calling for a reduction in federal funds for sanctuary cities, they shouldn’t have been — the feds were sending out warning signs even while Barack Obama was still president.

Buried in a 28-page Justice Department memo in May was a heads-up to cities and counties that members of Congress had asked the agency to “examine whether jurisdictions with sanctuary policies were in compliance with federal immigration laws as part of the upcoming grant process.”

The memo also said that if the Justice Department “receives information that indicates that the applicant may be in violation of any applicable federal law, that applicant may be investigated, and ... may be subject to criminal and civil penalties.”

County and city legal departments throughout the Bay Area were still trying to figure out what the warning meant for them when Trump changed the entire discussion with his executive order.

“Now, nobody knows what the rules will be,” said Alameda County Undersheriff Richard Lucia.

You might think Lucia’s agency is safe — Trump’s order cuts off federal grants to sanctuary jurisdictions “except as deemed necessary for law enforcement purposes” — but the language is so vague, no one knows for sure.

One unknown: What exactly amounts to refusal to cooperate with the federal Immigration and Customs Enforcement agency?

For example, in the past six months, ICE has asked San Francisco for the release dates on 41 people in its jail. Sheriff Vicki Hennessy hasn’t said no — she simply hasn’t responded to any of them, after determining that none of the cases fell within the city’s guidelines for cooperating with the feds.

How the new administration responds to that lack of response is what everyone is waiting for.

And finally: Yes, that was former Police Chief Greg Suhr, cooling his heels waiting for a table at Original Joe’s in North Beach the other night, while District Attorney George Gascón — whose push for police reforms helped force Suhr’s resignation — was hosting a large gathering of D.A.s in town for the Association of Prosecuting Attorneys convention.

“No big deal,” Suhr says.

San Francisco Chronicle columnists Phillip Matier and Andrew Ross appear Sundays, Mondays and Wednesdays. Matier can be seen on the KPIX TV morning and evening news. He can also be heard on KCBS radio Monday through Friday at 7:50 a.m. and 5:50 p.m. Got a tip? Call (415) 777-8815, or email matierandross@sfchronicle.com. Twitter: @matierandross