The inquiry has demanded the unredacted messages, along with diaries and notebooks, be handed over by Thursday.
The Cabinet Office argues some of the material is not relevant, but opposition parties say it should be disclosed in full so the inquiry can decide what is relevant.
Mr. Johnson is among those who will give evidence to the inquiry, which is due to start hearings in two weeks.
The inquiry has extended a deadline for the material to be handed over from 16:00 on Tuesday to 16:00 on Thursday.
Opposition parties say the inquiry should have the material in full so the inquiry can decide what is relevant to its investigations.
The Cabinet Office has raised concerns that releasing Mr. Johnson's WhatsApps in full could set an unwelcome precedent and have a "potential adverse impact on policy formulation in the future." The government is confident in its position and is concerned the unredacted messages would reveal personal information and breach privacy requirements.
The Cabinet Office is facing criticism for its handling of the Covid Inquiry, which aims to identify lessons from the government's handling of the pandemic.
The inquiry is facing questions over the release of messages between Boris Johnson and his advisers during the pandemic, with some saying it is a cover-up to save embarrassment for ministers.
The former head of the civil service, Lord Kerslake, has criticized the Cabinet Office's position, calling it "misguided." The inquiry is scheduled to begin public hearings in two weeks and will investigate issues including lockdowns, decision-making, and the protection of clinically vulnerable people.
LONDON DAILY ARCHIVE
Cabinet Office Denies Cover-Up Allegations Over Release of Johnson's COVID Inquiry Messages
The Cabinet Office has denied accusations of a cover-up over the release of former Prime Minister Boris Johnson's WhatsApp messages to the COVID Inquiry.
30 May 2023 · 23:10 UTC
