Babcock (BCKIF) shares fell to the bottom of the FTSE 100 Monday after officials axed a cleanup contract with the engineering firm and its U.S. partner, Fluor Corporation (FLR) - Get Report

The the U.K's Nuclear Decommissioning Authority (NDA) set the clock ticking on a two year notice period that will see the Babcock and Fluor contract, which is serviced by joint venture Cavendish Fluor Partnership, come to an end after just five of the fourteen years.

Both Babcock and the NDA said the work involved in cleaning the 12 nuclear sites was "materially different" to the original terms of the contract.

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For Babcock, the decision has shaved £800 million ($1 billion) off of its £21 billion order book and will have an annualized revenue impact of £100 million from the year 2020/21.

Babcock shares fell by 3.5% during early trading in London, to change hands at 875.5 pence, outstripping the 0.98% loss of the Stoxx Europe 600 Industrial Goods & Services index.

The contract in question is for the decommissioning and cleanup of the U.K.'s first fleet of nuclear power stations dating back to the late 1950's, comprised of twelve reactors dotted up and down the country, which have reached the end of their lives.

The NDA has endured one legal battle over the cleanup work which, in 2016, saw it settle with U.S. firms, Energy Solutions and Bechtel, over allegations that it did not follow proper procurement procedure in the £6.1 billion tendering process that took place in 2012.