Fintech firm Square is rolling its payroll services into a mobile app, and it briefly sent payroll stocks like ADP and Paychex lower.

It's a mobile version of the payroll offerings Square launched in 2015 — and another step in Square's efforts to handle every stage of small business finances.

"The app works just like the web experience. Import your timecards or enter hours, submit your pay run, and leave the rest to us (we'll take care of filing, paying, and withholding your payroll taxes). And now you can easily do all of this on your mobile device, no matter where you are," the company said in a blog post announcing the Square Payroll App.

Shares of ADP shed 1 percent in midday trading but erased nearly all of those loses by market close. Paychex shed 1 percent during the session.

Square, meanwhile, extended earlier gains following the announcement and ended trading nearly 11 percent up.