US mobile payments firm Square filed privately for an IPO, according to Bloomberg, citing sources, in what would be an unsurprising move if confirmed.

Square processed $30 billion in payments from its merchant customers in 2014, although the actual amount it makes from the process is considerably smaller.The firm has been attempting to upsell its customers on higher-margin additional services.

Under the Jumpstart Our Business Startups Act in the US, companies with less than $1 billion in revenue can file for an IPO with the US SEC privately, rather than undergo the public process used by larger firms.

There has been speculation for some time about Square going public.

The firm’s core service, which is called Square Register, enables small businesses to transform a smartphone and tablet into a cash register by adding a card reader.

Square’s service has proved popular but barriers to entry are low and it faces a horde of rivals.

The firm declined to comment about a possible IPO.