Apple reportedly held internal discussions to acquire or partner with Discover Financial Services, Bank Innovation has learned.

Google and Facebook have also considered working with Discover in recent months, our payments industry sources say.

Apple declined to comment for this piece.

The Discover acquisition idea at Apple, which reportedly took place about a year ago, did not go far enough for the technology company to even submit a bid to acquire the company, however. The contemplated acquisition was apparently a backup plan for the tech giant in case it could not reach a deal with issuers and other networks to partner on Apple Pay’s launch. Discover would have cost Apple about $37 billion, based on Discover’s current market capitalization.

So what’s with Discover that all four of these tech giants would consider acquiring it? One partner: China UnionPay.

In 2005, Discover and China UnionPay signed a long-term contract, forging a partnership between the two FIs. At the time, the agreement only let Discover cards work at UnionPay ATM’s and point-of-sale terminals. In 2007, Discover agreed to accept UnionPay cards at any Discover merchant in North and South America. The partnership expanded again in 2013 to accept card-not-present transactions using UnionPay cards, meaning that UnionPay customers that used mobile wallets would also be able to make purchases on Discover’s network.

The strengthening ties between Discover and China UnionPay have worried American financial institutions, according to sources who spoke to Bank Innovation. China UnionPay transaction volume is exploding in the US, and FI’s are worried that a tech company could bypass the card issuers or networks by partnering or acquiring Discover to gain access to China UnionPay. And that is apparently what Apple considered in 2013.

China UnionPay, which has been rumored to be in talks with Apple since last May, had a 4.1% marketshare in global credit card transactions last year, more than American Express, for example, according to the Nilson Report, which covers the credit card industry. Similarly, as of March, China UnionPay was the world’s largest card issuer in the world, with 3.5 billion cards in circulation, and responsible for $2.5 trillion in worldwide transactions for the first half of this year alone. That is compared to Visa’s $4.6 trillion.

(Parenthetically, it was purportedly only after that Apple-China UnionPay deal rumor surfaced that the card issuers here in the US took Apple seriously and inked a deal with the tech company for Apple Pay, sources say.)

It is important to note that Discover is not one of the network companies listed by Apple at as an Apple Pay partner during the venture’s launch last week, even though there has been talk since the Apple Pay announcement that Discover is negotiating with Apple. We are not certain what to make of these facts.

Experts who have spoken to Bank Innovation on the condition of anonymity due to the sensitivity of the topic think that Discover and even American Express remain partnership targets for tech companies interested in getting into the payments industry. An acquisition, however, is less likely. Not many companies — outside of Apple — can afford a $37 billion acquisition, which is the likely price for Discover. And American Express would be even more costly. Besides, most tech companies shy away from becoming a regulated financial institution because of the compliance issues and costs. But, if companies reach agreements with the issuers and networks, look for tech giants to once again consider an acquisition of Discover.

UPDATE: Sources tell Bank Innovation that the Apple and China UnionPay should be announced in October and that a Discover deal is likely as well.