It froze service for some partners this week, citing the need to ensure employee safety and prioritize critical shipments.

Alternative couriers such as eShipper and ShipTime act as middlemen between smaller e-commerce companies and large carriers including Purolator and UPS. The couriers bundle packages sent by small businesses to secure lower rates than the mom-and-pop shops could get through individual orders with the big players.

Now, eShipper is among the outfits temporarily barred from sending packages through UPS and the Canada Post-owned Purolator.

A notice sent from eShipper to clients and obtained by The Canadian Press says no shipments will be processed or moved by these carriers for 48 hours, starting Wednesday.

UPS did not respond to requests for comment.

The temporary bans speak to a shipping network strained to the breaking point, with implications for customers and shippers -- including eShippers 22,000-plus clients.

One of them, Montreal-based Felix & Norton, which ships gourmet cookies across the country, says the cargo halt and broader postal strike fallout could cost the company its whole holiday season.

This is absolutely insane and infuriating for everybody that doesnt even use Canada Post, chief operating officer Simon Paquin said, stressing the ripple effects of the work stoppage.

Most of Felix & Nortons business relies on shipped cookies rather than baked goods bought in-store, putting it among the retailers frantically searching for workarounds.

Big carriers such as Purolator, UPS, FedEx, Canpar and DHL are not equipped to pick up all the slack left by the Canada Post shutdown, said Paquin.

Theyre overloaded, Im hearing, until after the holidays ... we cant even process orders anymore because theres no shipping available.

The bakery is scrambling to arrange alternate deliveries in Montreal and Toronto by last-mile carriers, which typically deliver packages from a shipping hub to the buyers doorstep.

But lets say youve got to deliver something in the north of Quebec, you just cant anymore. I will lose a lot of business for sure, he said.

Canada Post said Thursday it was reviewing new counter-proposals submitted by the union representing more than 55,000 postal employees, who walked off the job three weeks ago.

The sticking points include wages and a push to expand into weekend delivery, with the two sides in disagreement over how to staff the expansion.

Calls for federal intervention have been mounting from the business community, but so far the government has said its not stepping in.

Canada Post handled 296 million parcels last year, or nearly 811,000 per day. Thats a big hole for private operators to plug, even if it represents just 29 per cent of the parcel market, according to the Crown corporation.

Alternative shippers and last-mile couriers are among the few companies poised to benefit from the gap in the market left by Canada Posts absence -- territory it may have trouble reclaiming once the labour dispute is resolved.

Were just trying to keep up, said Kevin Ham, CEO of Chit Chats. The e-commerce shipping platform has acquired record numbers of clients over the past three weeks, he said.

And when delivery capacity shrinks, shipping prices rise -- all the more so during peak holiday demand.

Montreal-based pantyhose maker Sheertex has said alternative carriers, overloaded with orders, have implemented significant surge pricing on shipments.

This is where nimble startups with a van are going to try and step in wherever possible, said Ulrich Paschen, an instructor at the Melville School of Business at Kwantlen Polytechnic University in Surrey, B.C.

Obviously, the network that Canada Post has is not that easily replicated. But I know that in a number of areas, Canada Post will have to struggle to regain what theyve lost.

In the meantime, the strike may deter customers from shipping due to the backlogs and the cost, hurting small businesses further.

Well charge $80 to ship a $50 gift. And theyre like, That costs more than my gift, said Timothy Byrnes, director of Jet Worldwide, a parcel delivery firm.

Byrnes said some carriers are narrowing their profit margins in a bid to accommodate small shippers, but that the rates still cant match the low fees charged by Canada Post.

Even if they wanted to pay double the rate, UPS and Purolator are just saying, Sorry, were backed up.