The Congressional Black Caucus is voicing strong opposition to two key political reforms being sought by presidential candidate Bernie Sanders in the run-up to the Democratic National Convention: abolishing superdelegates and opening up Democratic primaries and caucuses to independent voters.

Sanders is seeking to leverage his unexpectedly strong showing against Hillary Clinton in the Democratic presidential race this year to secure a series of policy and political objectives. Although none of the political reforms Sanders is seeking would affect his standing now, they are rooted in his frustrations with the contest against Clinton.

As of Sunday night, 587 superdelegates had announced their support for Clinton compared with 48 for Sanders, who sought to make a virtue of running against the “political establishment.” As a rule, the senator from Vermont also performed better against Clinton in primaries and caucuses where independent voters could participate.

In a letter sent to Sanders and Clinton on Saturday, the Democratic members of the Congressional Black Caucus said they oppose changes in both areas.

The Democrats utilize a system under which candidates win pledged delegates based on their performance in primaries and caucuses, but also seek support from superdelegates, Democratic elected officials and other party elites who have a say on the nomination but are not bound by the results in their states.

The letter, first reported by Politico, said that the current system “has worked quite well” because it allows members of Congress to serve as superdelegates “without the burdensome necessity of competing against constituents for the honor of representing the state during the nominating process.”

“There is no need to succumb to the pressure of a few individuals to make this change,” said the letter, signed by Rep. G.K. Butterfield (D-N.C.), chairman of the Congressional Black Caucus.

The letter also said that opening up primaries to voters who aren’t Democrats “would dilute minority voting strength in many districts across the country.”

Although participation rules for primaries and caucuses are set by states, the DNC could exert some influence over the process by providing incentives for states to open up their contests.

The letter could have resonate with Clinton, who soundly defeated Sanders in most states with sizable African American populations.

Besides Clinton and Sanders, copies of the letter were sent to DNC Chairman Debbie Wasserman Schultz (Fla.), Senate Minority Leader Harry M. Reid (D-Nev.) and House Minority Leader Nancy Pelosi (D-Calif.).