Oregon Sens. Jeff Merkley and Ron Wyden have announced plans to block President Trump's nominee for the San Francisco-based 9th Circuit Court of Appeals.

In a letter to the White House on Thursday, the two Democrats said they do not intend to return blue slips for Ryan Bounds "or any other nominee that has not been selected through our judicial process."

"As you are aware, in May we wrote you to explain Oregon's long bipartisan tradition of working together to identify the most qualified candidates for judicial vacancies," they wrote.

"As senators charged with the task for advice and consent in the selection of candidates, we take our responsibility to identify and recommend candidates to fill Oregon judicial vacancies very seriously."

Under the "blue-slip" process, the home-state senators of a judicial nominee can object to the nomination by refusing to return the blue-colored paper of support to the Senate Judiciary Committee.

Merkley and Wyden said Trump has demonstrated he's only interested in their input if they willingly pre-approve his preferred nominees.

"The judicial selection process is not a rubber stamp and the insinuation that our offices were purposely delaying the process is an indication of the partisanship with which you are pursuing this nomination," they said.

Bounds, who currently serves as the assistant U.S. attorney for the District of Oregon, was part of Trump's seventh wave of judicial nominations on Thursday.

Earlier this week, Sen. Al Franken (D-Minn.) reportedly said he will oppose David Stras, Trump's nominee to serve on the 8th Circuit Court of Appeals.

Senate Democrats eliminated the minority party's power to filibuster judicial nominees for lower courts in 2013 and Republicans eliminated the process for Supreme Court picks last year, leaving the blue-slip tradition the only way for senators to veto controversial nominees.