Story highlights Ted Cruz is not releasing his delegates in at least one key state in advance of the Republican convention

Cruz sent a letter to the Kansas Republican Party informing them that he plans to keep the delegates he won bound to him

Washington (CNN) Ted Cruz is not releasing his delegates in at least three states, a sign he may hold onto some clout at this summer's Republican National Convention.

Cruz sent a letter to Republican state parties in at least Kansas, Oklahoma and Texas on Monday informing them that he plans to keep the delegates he won bound to him.

Kansas delegates are particularly key: They are required to remain with whomever they are pledged to until the candidate officially releases them -- unlike most states, they are not allowed to vote their conscience unless explicitly given permission, which Cruz isn't giving them.

"Although I have suspended my campaign for the Republican Party nomination for President of the United States, I do not release any Republican National Convention delegates bound to me as a result of the 2016 delegate selection process that took place in your state," Cruz wrote in a letter to Kelly Arnold, the chair of the Kansas GOP and obtained by CNN.

Oklahoma's Republican Party received a similar letter from the Cruz campaign, state GOP chair Pam Pollard told CNN. As did the Texas GOP, according to executive director Kyle Whatley.

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