WINNIPEG -- A trade dispute in the western provinces grew Monday when the Saskatchewan government said Manitoba could have avoided any trouble long ago by joining a regional trade agreement.

"Manitoba has been repeatedly invited to become a member of the New West Partnership, but they have chosen not to do so," Saskatchewan Trade Minister Jeremy Harrison said in a written statement.

"We would continue to welcome Manitoba's membership in the New West Partnership, which would address the issue raised by Manitoba."

Saskatchewan, Alberta and British Columbia established the partnership in 2010 in an effort to reduce trade, investment and labour barriers. Manitoba opted not to join.

In recent weeks, two of the partnership provinces have started giving preferential treatment to companies within the trade zone. Saskatchewan has started limiting some Crown corporation contracts to businesses within the zone and Alberta has announced preferential pricing for craft breweries based in the three provinces.

The move upset small beer companies further east. The Toronto-based Steam Whistle brewery called Alberta's move protectionist and divisive.

"There seems to be a bit of a pattern here recently with Manitoba having these issues," Harrison said after question period at the Regina legislature on Monday.

"They would all be solved if Manitoba moved forward with joining the New West Partnership. The invitation has been an open one and we've had a number of discussions extending that invitation to them over the years."

Manitoba's minister for jobs and the economy, Kevin Chief, said last week that the Saskatchewan move surprised him.

On Monday, he said Manitoba has been focusing its energy on renewal of a trade deal that covers all provinces -- the Agreement on Internal Trade -- which is to be revamped by next spring.

"We are in the centre of the country ... and it's important for us to do trade as much to the east -- in fact, we do more trade to the east --than we do to the west."

Chief said he had reached out to Harrison and was hoping to talk to him shortly, but Harrison said he had not heard from Chief directly.

"Provinces of every political persuasion deal with each other every day in a professional and respectful way," Harrison's statement read.

"The fact that the government of Manitoba chose to raise these matters in the media without any previous communication at either the official or political level is disappointing."

Chief did not say whether Manitoba is considering challenging Alberta and Saskatchewan's recent restrictions.

Manitoba Opposition Leader Brian Pallister has called on the government to join the New West Partnership. He has said there is no reason the province cannot be part of both regional and national trade agreements.

-- With files from Jennifer Graham in Regina