WASHINGTON  A leading Republican senator maintains that President Obama is violating a campaign promise with his claim that he can bypass whistle-blower protections for executive branch officials who give certain information to Congress.

The lawmaker, Senator Charles E. Grassley, Republican of Iowa, sent a letter to Mr. Obama on Friday that condemned a signing statement the president attached to the $410 billion catchall spending bill he signed into law last week.

A signing statement, occasionally issued by presidents upon their signing a bill, is a document that instructs executive branch officials on how to carry out the new law. In this statement, Mr. Obama flagged a provision that protects officials who give information to Congress about their jobs or agencies. He said the statute could not limit his power to control the flow of certain information to lawmakers.

“I do not interpret this provision,” he wrote, “to detract from my authority to direct the heads of executive departments to supervise, control and correct employees’ communications with the Congress in cases where such communications would be unlawful or would reveal information that is properly privileged or otherwise confidential.”