Civil rights advocates filed a lawsuit in San Francisco on Thursday against the federal government in an attempt to get information about how many detained asylum seekers are denied parole and how such decisions were made.In the lawsuit, filed in U.S. District Court, the American Civil Liberties Union ’s Immigrants’ Rights Project, the Center for Gender and Refugee Studies at UC Hastings College of the Law and others want to know why fewer asylum seekers are being offered parole.

The groups hope to get statistics from U.S. Immigration and Customs Enforcement on the parole decisions for detained asylum seekers from 2010 to now and documents detailing the process for coming up with those decisions, the ACLU of Northern California said.

“We’ve seen a nationwide shift in detention policies for arriving asylum seekers who are found to have a credible fear of persecution, and we need this information to find out what has changed and why,” said Angélica Salceda , an attorney with the ACLU of Northern California. “The public has a right to know if ICE has reversed its policy.”

Asylum seekers who present themselves to immigration authorities at a port of entry are interviewed and have their cases reviewed, said Michael Tan , an attorney with the ACLU Immigrants’ Rights Project.

If they are found to have a credible fear about being sent back to their country of origin, then they’re detained and referred for a full hearing in immigration court, Tan said.

But in 2010, the agency created a directive that called for asylum seekers with no flight risk or danger to the community to be released pending decisions on their cases, according to the ACLU. Since at least 2014, however, such asylum seekers have been denied parole, they said.

In 2012, the ACLU said, ICE reported granting parole to 80 percent of asylum seekers who established a credible fear. Just under 50 percent were granted parole three years later, the group said.

The lawsuit was filed under the Freedom of Information Act. In two previous FOIA requests, ICE has released only partial records, Tan said.

“We are concerned that this turn toward locking up asylum seekers is meant to deter efforts by people who are fleeing persecution, extreme violence, and even death,” he said.

An ICE spokesman said that as a matter of policy the agency does not comment on pending litigation.

Hamed Aleaziz is a San Francisco Chronicle staff writer. Email: [email protected] Twitter: @haleaziz