Some U.S. border agents have quietly begun refusing to process work visas for Canadians already working in the country, a change that is confounding immigration lawyers and could pose problems for big Silicon Valley employers that frequently move tech workers between Canada and the U.S.

Canadians seeking to renew documents used for intracompany transfers have until recently applied at airports and border stations staffed by U.S. Customs and Border Protection.

The border agency, part of the Department of Homeland Security, is now directing Canadians to file renewals for L-1 visas with a different agency, Citizenship and Immigration Services, in a far more cumbersome process, according to an email sent by a border officer in Toronto obtained by The Chronicle.

It’s just the latest change that appears to throw bureaucratic obstacles in the way of bringing high-skilled workers to the United States.

Attorneys for those workers from north of the border say they are scrambling to make sense of the change, in the absence of a memo from the agency, and adjust their strategies for landing the transfer visas.

“Welcome to our nightmare. All of a sudden, they don’t like Canadians,” said Lisa Spiegel, an attorney at Duane Morris in San Francisco and head of the firm’s immigration practice group.

A spokesman for Customs and Border Protection did not respond to a request for comment. A spokeswoman for the immigration agency referred The Chronicle to the border agency.

People who lead a team of employees as an executive or a manager at a company based in the U.S., but who are working remotely at an affiliate office, may apply for an L-1A visa after one year of work. Others who bring some specialized knowledge to the business are eligible for a similar visa known as the L-1B.

The L-1 visas are commonly used by big tech companies to bring in sales and engineering leaders from their offices abroad. HP, Google, Cisco and Apple were among the top sponsors of L-1 visa holders in fiscal year 2017.

Canadians have been able to apply for L-1 status at the border — in an international airport or at a road crossing — without having to file a petition with the immigration agency, which handles visas more broadly than the border agency.

Filing a petition can take several months, but a Canadian who qualifies for L-1 status can, for example, arrive for a flight from Toronto to San Francisco a few hours early, meet with a border officer, and get the visa status squared away.

For years, it didn’t matter whether the person was applying for the first time or nearing an expiration date and filing for renewal, said immigration attorney Ron Matten.

“There was always this little quirk: You don’t call it an ‘extension,’” Matten said. “They’ll just go visit Canada and on their way back in, say, ‘Here’s my application for a new period of time.’”

That started to change a couple months ago, according to Matten, who is also chairman of the American Immigration Lawyers Association’s Canada chapter.

“There were reports out of Calgary that people were being turned away because they were told, ‘This was not a new application. This is a renewal. We don’t process this.’ Which is basically wrong,” Matten said.

As the Trump administration has pushed a “Buy American, Hire American” campaign, immigration officials have raised other hurdles for those seeking permission to work in the United States in recent years.

For example, applications for the H-1B visa commonly used for high-skilled workers have been receiving more requests for evidence seeking further proof of their eligibility. The H-1B process has been revamped to give preference to applicants with master’s degrees or doctorates from U.S. universities. And immigration attorneys say border officials are more closely scrutinizing petitions for the TN visa, a work permit for citizens of Canada and Mexico.

Justin Parsons, managing director of the Erickson Immigration Group in Arlington, Va., said two of his clients, both high-level managers working for a financial services company in the U.S., traveled to Vancouver a month ago to file new applications. Their L-1 status was set to expire within a few weeks.

“They weren’t denied, but they were sent away,” Parsons said.

The clients were still allowed to enter the country on their previous status and then worked with Parsons to renew by mail. Still, Parsons and other immigration attorneys say they avoid going through the immigration agency when possible, saying they worry it will issue unnecessary requests for evidence. Little more than half of applicants are granted L-1 visas after receiving a request for evidence.

Data show that immigration officials approved 74 percent of L-1 petitions in the first quarter of 2019, down from 85 percent in fiscal year 2016, an analysis by immigration firm Fragomen found.

Clients also have the option of making an appointment at a U.S. consulate in Canada instead of applying by mail. There’s typically a wait time of a couple weeks, Parsons said, followed by a week or two of processing time.

The change is more of an inconvenience, immigration attorneys said.

Still, Parsons and other attorneys said the change could hamstring travel between the two countries for L-1 status workers.

“Any sort of delay to get back to their job is a huge issue for them and for us,” Parsons said. “Very rarely do our clients not have a place to be.”

Spiegel, the immigration attorney in San Francisco, is more concerned about how the change was rolled out.

“It would have been nice to have been told there was a policy change. But since the new administration came into effect, they’ve stopped a lot of the liaison meetings,” she said, referring to meetings between immigration attorneys and immigration program officers.

Parsons said he no longer counts on Homeland Security to alert the public to policy changes.

“It’s the nature of the current administration,” he said. “They don’t tell you why. They don’t tell you when. They don’t tell you the legal reason for it. They just do it.”

Melia Russell is a San Francisco Chronicle staff writer. Email: melia.russell@sfchronicle.com Twitter: @meliarobin