WASHINGTON - The Federal Intercarrier Commerce Bureau said Monday that any shop without a recorded voicemail refusal has constructively joined the automated retail conversation and must keep a dedicated line available for agents to ask whether a thing is in stock. In a filing posted to the bureau's docket, the agency said agents placed as callers for stock and price checks may treat the absence of a recorded opt-out as participation. Shops that have not left such a message are required to maintain a line that can receive those inquiries. "Silence is the most scalable form of consent," said bureau spokesperson Helen Brackett. "A merchant who has not left a recorded refusal has not withdrawn from the conversation." The Independent Shopkeepers Federation said members can opt out by leaving a voicemail, which the agents may call repeatedly to verify. The rule takes effect Oct. 1.