Democratic presidential candidate Bernie Sanders has accused the Democratic National Committee of tilting the party’s convention in favor of frontrunner Hillary Clinton, arguing that the committees have been filled with his rival’s supporters.

In a Friday letter to DNC Chairwoman Debbie Wasserman Schultz, Sanders said the convention committees don’t reflect the fact that he was won 45 percent of the pledged delegates awarded throughout the primary season thus far. The Vermont senator said Wasserman Schultz only appointed three of the 40 people he had recommended to sit on the convention’s standing committees.

Sanders also said Wasserman Schultz did not select anyone that his campaign had recommended to the Rules Committee of the Democratic National Convention, even though the individual chosen to be its chair is a supporter of Clinton. Sanders said the chair of the Platform Committee also supports his rival, and that both individuals are “aggressive attack surrogates” for her on the campaign trail.

“If we are to have a unified party in the fall, no matter who wins the nomination, we cannot have a Democratic National Convention in which the views of millions of people who participated in the Democratic nominating process are unrepresented in the committee membership appointed by you, the Chair,” Sanders wrote in the letter.

Sanders drops lawsuit against DNC over voter database breachhttps://t.co/sJeWTIfg1Zpic.twitter.com/ggNQTTVvbN — RT America (@RT_America) April 30, 2016

Sanders said the way the DNC chooses the appointees for the Drafting Committee, which establishes the Democratic Party platform, should be improved as well. He recommended that both his campaign and the Clinton camp choose seven members instead of four, as Wasserman Schultz has proposed, and that the committee chair be a consensus pick decided upon by the two sides.

As it stands, Sanders claimed the DNC’s process is “overtly partisan,” suggesting “it is not open to the millions of new people that our campaign has brought into the political process.”

If the DNC does not take steps to work with the Sanders campaign to address its concerns, the senator said his delegates would try to do so at the convention itself in July.

“If the process is set up to produce an unfair, one-sided result, we are prepared to mobilize our delegates to force as many votes as necessary to amend the platform and rules on the floor of the convention,” Sanders wrote.

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The DNC did not specifically respond to Sanders’ argument, though it released a statement saying his campaign, as well as Clinton’s, would be represented.

“Because the Party’s platform is a statement of our values, the DNC is committed to an open, inclusive and representative process,” the DNC said in a statement to Politico. “Both of our campaigns will be represented on the Drafting Committee, and just as we did in 2008 and 2012, the public will have opportunities to participate.”

This isn’t the first time Sanders has sparred with the DNC over the course of the campaign season. He has accused the DNC of showing bias towards Clinton in a number ways, including in scheduling the debates. He and his supporters have also often criticized the role of party officials and insiders called superdelegates. These individuals can throw their support behind any candidate they like, and hundreds of them have professed their loyalty to Clinton from the very beginning, including those from states that Sanders has won.

For her part, Wasserman Schultz has defended the nominating process, accusing Sanders of hypocrisy since he and his campaign have said they would try to flip some of the superdelegates in order to win the nomination.

“Bernie Sanders is wrong because we have had these rules in place since 1984,” Wasserman Schultz said in an interview with Bloomberg. “We have two types of delegates: we have the delegates that are pledged, that… represent voters based on the outcome, and then we have party leaders and other elected officials who have been in the trenches for a long time who have a role, appropriately so, in choosing our party’s nominee.”

Sanders has also complained that some states feature closed primaries, which are only open to registered Democrats, and not independents. He and his supporters have argued that anyone should be able to cast a vote during the nomination process, while the party has said Democrats should choose who the Democratic presidential nominee should be.