(Bloomberg) -- Czech billionaire Daniel Kretinsky’s £3.6 billion ($4.6 billion) takeover of the parent of Royal Mail on the eve of a UK general election looks set to unleash a struggle over the future ownership of Britain’s postal service.

The tycoon’s EP Group agreed to buy the shares it doesn’t already own in International Distribution Services Plc and to protect Royal Mail as a “key part of the fabric of UK society.” Kretinsky also pledged not to break up the group for at least three years and to deliver letters six days a week for the next five years. 

Shares of IDS rose as much as 4.4% to 335.2 pence in London trading Wednesday, still well below Kretinsky’s 370 pence-per-share offer, reflecting investors’ doubts over whether the sale will go through.

The deal, coming just days after the election was called, is likely to face opposition from UK politicians who have previously voiced concern about Kretinsky already owning a chunk of the former state-owned company. His stake is currently more than 27%.

The opposition Labour party, the favorite to win the July 4 election, has said it will examine the deal, which is worth £5.3 billion including debt.

“Royal Mail is an iconic British institution with a unique place in our society and infrastructure,” the party’s shadow business secretary, Jonathan Reynolds, said Wednesday. “Labour will take the necessary steps to safeguard its undeniable identity and place in public life.” 

Reynolds did welcome Kretinsky’s assurances, including a pledge that there will be no compulsory job losses.

IDS has accepted the offer, while calling on the government and regulators to relax strict rules around letter deliveries. Royal Mail has asked UK regulators to swiftly cut back its legal obligation to deliver letters across Britain six days a week. The regulator is considering reforms.

Royal Mail is grappling with a decline in letter writing and the rise in parcel deliveries tied to e-commerce. Members of the Communication Workers Union voted to accept a new pay deal last year after months of strikes, during which it accused management of prioritizing parcels over letters.

Kretinsky also committed to keeping the Royal Mail brand and maintaining IDS and Royal Mail headquarters in the UK. He will continue to recognize the unions.

“We remain to be convinced that this will be sufficient to secure support for whichever government gets to make the decision,” said Liberum analyst Gerald Khoo in a note. He said getting government approval under the National Security & Investment Act remains a “major hurdle” to the deal.

The current Conservative government has intervened in other deals recently, including the UAE-backed takeover of the Telegraph newspaper group. It also comes at a time when the political mood has soured on the privatization of UK public assets after a surge in sewage spills by water companies and delays and cancellations of trains.

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Kretinsky’s EP group said Royal Mail and logistics business GLS require further investment and “would be better placed to obtain and structure such investment as a private company.”

The Czech investor has slowly built up his IDS stake over the last few years, along with other investments across Europe as he diversifies away from energy. In the UK, he also has stakes in grocer J Sainsbury Plc and Premier League football club West Ham United.

(Updates with share price, Labour comment, chart and further detail throughout.)

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