House Speaker Paul Ryan says he's "disturbed" by former FBI lawyer Lisa Page's decision not to comply with a subpoena to be interviewed by two House committees behind closed doors Wednesday.

"She was a part of the mess that we have uncovered over at DOJ. She has an obligation to come and testify. If she wants to come and plead the Fifth, that's her choice. But a subpoena to testify before Congress is not optional. It's mandatory. She needs to comply," Ryan said after a regular House GOP conference meeting.

The House Judiciary and Oversight and Government Reform Committees are investigating whether there was bias in FBI and DOJ investigations into Hillary Clinton's email server and Russian meddling in the presidential election. Page, who exchanged anti-Trump text messages with FBI official Peter Strzrok during the Clinton email investigation, was asked to appear for an interview with the committees.

Get Breaking News Delivered to Your Inbox

Page's lawyer said the committee issued the subpoena on Saturday, July 7, and would have been asking her about material her lawyer said she had not yet been shown.

Ryan, asked about Page's decision not to testify Wednesday, said, "I am very disturbed by this. Congressional subpoenas for testimony are not optional."

Asked what the House is considering doing if Page doesn't comply, including holding Page in contempt, Ryan said Congress would "do what we need to do to protect this branch of government."

Page's lawyer Amy Jeffress told CBS News' Paula Reid that she and Page on Tuesday went to the FBI, her former employer, to review the materials that were sent to Congress, but they were not shown any documents after waiting more than three hours.

On Wednesday, though, Jeffress said that the Justice Department granted her access to the material "after 11 pm last night." And she also said Page has been cooperating with the probes, and she expected Page to appear before the committees "in the near future."

On Thursday, both panels will convene a joint session to hear public testimony from Strzok about the FBI investigation into Russian interference in the 2016 election. Strzok previously participated in a closed-door interview with lawmakers late last month after he was named in the DOJ inspector general's report on the handling of the Hillary Clinton email investigation.

The report criticized Strzok for communicating anti-Trump bias throughout the investigation, including an exchange in which Strzok told Page "we'll stop" then-candidate Trump from becoming president.