BERLIN (AP) – German Chancellor Angela Merkel and her center-left rival, Martin Schulz, are preparing for their only televised debate before the Sept. 24 election following a campaign that so far has lacked a head-to-head showdown between the two leading candidates.

Merkel, who heads Germany’s center-right Christian Democrats, has stepped up her campaigning in recent weeks as she seeks a fourth term leading Europe’s biggest economy. She has highlighted the country’s prosperity and sought to address conservative fears with a tougher line on policing and immigration.

In an interview published Saturday, Merkel said she wants to continue police checks introduced at Germany’s borders as a temporary measure in September 2015, a procedure the European Union says runs contrary to the bloc’s passport-free travel rules.

Merkel, 63, told daily newspaper Rheinische Post she’s confident the EU’s executive arm has “an open ear for our arguments” to extend the controls beyond their Nov. 11 expiration date. They began amid an influx of asylum-seekers that critics partly blame on the chancellor’s welcoming approach to refugees.

Germany’s Social Democratic Party unexpectedly nominated Schulz, 61, in January to challenge Merkel. He has been free to campaign full-time since he left his post as president of the European Parliament, the EU’s legislative body.

But Schulz has refrained from making sustained attacks on Merkel’s leadership, focusing instead on issues of social justice and pledging to get rid of U.S. nuclear weapons stationed in Germany.

In an interview published Saturday by daily newspaper Bild, Schulz said he wasn’t nervous about Sunday’s debate, which will be broadcast live by four of Germany’s main television stations.

The former bookseller, whose highest elected position in Germany was as mayor of the small western town of Wuerselen, acknowledged that his party had suffered two “very, very difficult defeats” in recent regional elections. He insisted that the national contest could swing his way because many voters are still undecided.

A poll published Friday by public broadcaster ZDF put the Social Democrats with 22 percent support compared to 39 percent for Merkel’s bloc. The survey of 1,309 German voters had a margin of error of up to 3 percentage points.

The parties are currently in a coalition at the national level.