HARRISBURG — Allentown Mayor Ed Pawlowski is expected to announce today that he will run to challenge U.S. Sen. Pat Toomey’s re-election bid, creating the potential for a contested Democratic Party primary in 2016.

Pawlowski was calling party officials to inform them of his decision, Democratic Party Chairman Jim Burn and others said. Pawlowski planned an announcement today, but political adviser Mike Fleck would not say what Pawlowski would announce.

The mayor of Pennsylvania’s third most populous city briefly tested his statewide electoral prospects in last year’s governor’s race, but he never made the ballot and dropped out several months later after having fundraising difficulties in a big field of candidates.

Jonathan Saidel, Philadelphia’s former city controller, said he spoke with Pawlowski about his decision and that it will be important for a candidate to start fundraising as early as possible in a federal system that places strict limits on individual campaign donations.

Pawlowski, 49, has been Allentown’s mayor since 2006, overseeing a huge expansion of development downtown, anchored by the PPL Center arena, and steering Allentown through the Recession. Under Pawlowski, Allentown leased its water and sewer system, getting an up-front payment that allowed it to slash millions off its annual pension obligations and avert huge tax increases.

“I think Mayor Pawlowksi has a great story to tell,” Saidel said.

The winner of the April 2016 Democratic Party primary will go on to challenge Toomey, a Republican and first-term senator from suburban Allentown who was elected in 2010.

Toomey, a former businessman and investment banker, is expected to be a formidable candidate and to have backing from free market and anti-tax groups that have a lot of money to spend to influence elections. Toomey’s campaign spent nearly $17 million to win the 2010 campaign.