UPDATE 1-Alberta to intervene in antitrust review of Rogers, Shaw deal

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OTTAWA, July 5 (Reuters) - The Canadian province of Alberta plans to intervene in a competition review of Rogers Communications Inc's C$20 billion ($15.33 billion) purchase of Shaw Communications Inc, the provincial attorney general said on Tuesday.

The companies "have significant presence in Alberta's telecommunications market and their successes and failures will impact Alberta's consumers, workers, and, potentially, other aspects of Alberta's economy," according to a notice posted on the competition tribunal's website.

The Alberta government is intervening under a provision of the competition act that prohibits illegal trade practices such as forming a cartel.

Shaw, which has two million wireless customers in Alberta, is based in Calgary, while Rogers is based in Toronto.

Canada's antitrust authority has sought to block the deal on the grounds that it will hurt competition in the sector in Canada.

The Competition Bureau Canada, Rogers and Shaw began their two-day mediation process at a tribunal on Monday.

Rogers shares fell 1% to C$61.69 on the Toronto Stock Exchange at midday on Tuesday, while Shaw fell 0.14% to C$37.88.

($1 = 1.3046 Canadian dollars)

(Reporting by Ismail Shakil in Ottawa and Divya Rajagopal in Toronto; Editing by Chizu Nomiyama and Deepa Babington)