Without debate or discussion, the Dallas City Council on Wednesday unanimously ordered a special election for two contentious amendments to the Dallas City Charter.

Most council members oppose both charter amendment propositions, which will appear on Dallas' May 9 ballot along with district-level council elections.

The council, however, had little choice in calling the elections. The Dallas city secretary's office has certified signature petitions from separate groups that successfully collected more than 20,000 valid Dallas voter signatures to trigger the referenda.

The first proposition seeks to prohibit Dallas from owning a convention center hotel – something the city is today in the process of trying to build.

The second proposition aims to all but require Dallas to conduct a citywide referendum each time the city wants to give $1 million or more in subsidies to private developers of hotels, condominiums and retail facilities. Under the amendment, 500 Dallas voters would have to sign a petition to call a citywide referendum on any applicable subsidy.

Mayor Tom Leppert has vowed to wage aggressive campaigns – including advertising blitzes – against both propositions. He argues that both would harm Dallas' efforts to expand the city tax base by attracting tourism and new investment.

But opponents of Dallas' proposed convention hotel, which is slated for construction but yet unfunded through a sale of revenue bonds, maintain that taxpayers will ultimately subsidize the facility if it loses money.

Citing government transparency and accountability, New York-based labor union Unite Here sponsored the drive to place the subsidy limitation on the ballot.

But Leppert and other council members say Unite Here is trying to exact revenge on the city for not granting the union work guarantees in the planned convention hotel.

Council members on Wednesday listened to a plan for planting trees in Dallas that urban foresters hope will lead to a significant increase in the city's tree canopy.

The plan presented by the Texas Tree Foundation identified five tracts to demonstrate the benefits not simply of planting trees, but of planting them in areas where they can best reduce rainwater runoff, collect emissions from cars and reduce ambient air temperatures.

The city currently has a tree canopy of around 8 percent. Ideally, that canopy would grow to 30 percent, the council learned.

Plantings could be targeted in areas of high traffic congestion, near "hot" buildings that generate and hold heat at their rooftops, and near water sources, among other sites.

The Tree Foundation did not request city funds. It expects to seek private and federal money to achieve its urban forestry goals.

dlevinthal@dallasnews.com; rbush@dallasnews.com